Bloopers I recall:
A Stormtrooper bangs his head on a door in ANH (now made canon by Lucas!).
Harrison Ford grabs Carrie Fisher's breast in ROTJ in the bunker scene.
You can see Harrison Ford's makeup has come off his chin and smeared on his trooper armor in ANH (in the scene where they're pinned down in the hallway before going into the Garbage Chute).
In a few shots you can still see expelled shell casings (or whatever they are, they used blanks) from the trooper rifles used in ANH.
In ROTJ, as Lando is flying the Falcon inside the Death Star II ("that was too close") the satellite dish is smashed off. Let later it's visible again.
Oola the slave dancer at Jabba's has her breast pop out of her outfit in ROTJ.
Panda Boba's (?) arm that's cut off and left in the cantina by Ben in ANH is wrong (it's actually "Wolfman's" arm, and you can see the original arm on the Behind the Magic CD-ROM in an early take of the Cantina sequence).
"Made in England" supposedly discernable on the needle of the "Torture Droid" that approaches Leia in ANH.
Obi-Wan's lightsaber "fizzles out" for several frames during his duel with Darth Vader in ANH as he faces the camera, revealing the prop rod that was used. Also in a shot where the stormtroopers are going over to "watch the fight" Vader (on the left) is seen with an uncolored lightsaber prop.
Luke's lightsaber changes color in the scene where he "trains" on the Falcon in ANH.
Kenny Baker Jr's flesh is visible inside R2D2's eyepiece in ANH (inside the Sand Crawler).
"Bat creature" in Cantina scene has one shot where you can see through the transparent eye of the mask. The actor later puts a cup to a part of the mask as if to drink that is not the creature's mouth (probably the actor's mouth inside the mask).
A black pedestrian extra crosses the screen several times in the scenes with Obi-Wan and Luke entering Mos Eisley and talking as they prepare to enter the cantina (by my count he crosses about four or five times!) in ANH. There may be more!
Visible "boots" on actor Peter Mayhew's feet under his Chewbacca costume visible in ESB as he moves through Cloud City.
Luke has a tear stream down his face in the scene where views the dying Anakin in ROTJ. In the next shot the tear is gone.
The "pole" holding up the Falcon model leaves an artifact against the "glow" of the doorway of the hangar as it is pulled into the Death Star in ANH. Look below the ship as it comes in to see it.
Inconsistent placement of those metal objects near Leia's hologram, when Obi-Wan is viewing the complete message in ANH (changes between shots).
Non-droid corpses literally the arena seem to be missing in shots of the droids talking on Geonosis after the battle in AOTC. There's also a conspicious lack of Gungan bodies after the battle in TPM as well.
During the battle between Dooku and Anakin in AOTC, Obi-Wan's body seems missing in some shots. Likewise with Yoda and Dooku (the bodies of Anakin and Obi-Wan seem missing).
The "Death Star plans" computer diagram displayed on screen in ANH after R2D2 plugs into the Rebel computer is inconsistent with the Death Star model we constantly see everywhere else in the movie.
The actor playing Wedge during the Rebel briefing in ANH (who says "that's impossible, even for a computer!" and Luke talks to) is not the same actor that plays him in the actual space battle and elsewhere in the trilogy. It could be rationalized that this is simply a different pilot, but we never see that pilot again!
R2D2's head panels are black in some space shots, but blue in others in ANH, inconsistently fixed in the later editions. (Possibly also in ESB and ROTJ).
Possibly bloopers, depending on how you view the Star Wars Universe:
When Obi-Wan pulls off his amazing comeback at the end of his duel in TPM, Darth Maul's saber is on, then off, then on again (this was explained on another site as Obi-Wan using the Force to turn off his lightsaber, which I really like, but still!).
One of the "dorsk" (?) aliens who is arguing with another alien just like himself in the Cantina has one "alien" hand and one "human" hand.
A quick view through a stormtrooper's transparent eyepiece let's us see through the mask in ANH (the scene of the troopers trying to stop Obi-Wan and Luke in Mos Eisley).
Several instances of Stormtrooper helmets not being on all the way (actor's exposed skin visible): in ROTJ, ESB and ANH (see especially ESB where the two stormtroopers drop Solo off after his interrogation and one of them almost loses his helmet because Han's arm brushes against it).
One end of Darth Maul's lightsaber blade passes through his own hand (without damage) in TPM (in the shot where the two Jedi leap across a catwalk to attack him).
Several instances of the shadow of a lightsaber blade is visible, such as in ROTJ (final duel between Vader and Luke) and in ROTS (during the duel with Count Dooku).
In the scene where Luke is watching the "message" of Princess Leia in the Lars home, Threepio can be seen in the background stumble and nervously (?) rub a rag against his thigh.
The top portion of Vader's helmet flaps in the wind in the scene where he tries to get Luke to join him in ESB.
A small explosion appears in a crevice of an asteroid ahead of the Falcon as it is pursued by TIE Fighters, yet we see no cause (like a laser blast) for the explosion in ESB.
Several instances of "turbolasers" and hand blaster/vehicle blaster weapons doing visible damage (or sparks) before the colored bolt "hits" its target (See ROTJ when Luke's hand is shot by one of Jabba's men, a shot almost hitting Yoda during a battle on Kashyyk in ROTS, etc.)
In the Special Edition, the old Sy Snootles puppet was replaced by a CG version, with many visible differences (no feather headdress, missing "fangs" and different looking eyes). Despite the replacement, the old Snooty is still visible in a few pan over scenes in Jabba's palace in ROTJ standing in the background (it's dark, but possible to see).
General Grievous's lightsabers have the same hilt designs as Anakin and Obi-Wan's in ROTS. Supposedly his other lightsabers appear to be the same as hilts used by other Jedi (and, I assume Jedi that aren't dead yet by this time).
How did Luke and Obi-Wan get their clothes back after the garbage masher scene in ANH? Did the stormtrooper boots really fit over their original boots?
What happened to all those laser shots that Vader fired at Luke's X-Wing in ANH during and just before the part when Han Solo was shooting up his wingmen? (Remember Vader was supposedly locked on!)
In ANH when Han and Chewie meet back up with Leia and Luke ("We ran into some old friends") you can see Leia and Luke's shadows as they are waiting just off camera right before they come on. Could be rationalized, but would be somewhat silly.
The same cloud of ships flies by Chancellor Palpatine's window in almost the same way throughout the same scene in his office in AOTC.
In ROTJ after Han Solo's ruse to get the troopers out of the bunker, the officer in charge says "Send three squads to help" yet we only see 15 extras (at most) come out of the bunker. Squads in the Empire might just be that small, of course.
In the scene where we first see Vader in ANH, his helmet looks grimy or at least non-reflective. Yet in a later shot where he's talking with an Imperial Officer, his helmet looks shiny. When did he have time to polish it up?
Perhaps not true 'bloopers' but still:
In the Special Edition, with the extended "Vader's arrival" when his shuttle lands, we see a reversed unused shot from ROTJ (note Moff Jerrerod on the second Death Star... which in this scene is supposed to be the Executor!).
In the Special Edition, Luke Skywalker screams as he falls through the shaft in ESB. The scream is exactly like the one that the Emperor utters in ROTJ as he falls. This was removed again in the subsequent 2004 edition.
Billy Dee Williams appears to mumble one of his lines in the space battle in ROTJ, as part of it was cut off by accident. This was corrected in later editions ("We're sure in the middle of it now!").
Obvious cardboard Lando hanging onto the bottom of the Skiff in ROTJ as Luke does his famous leap from one to the other.
Huge section of painted on stormtroopers visible during the Emperor's arrival shots in ROTJ.
Obvious black touch-ups on the film to cover holes in the Emperor's mask/hood ensemble in ROTJ ("Emperor's slugs").
Dozens of visible "matte boxes" around objects in space (see especially the battle over Endor in ROTJ).
Several instances of stars "shining through" ships in ESB (especially the Falcon or a Star Destroyer) and ROTJ. Possibly fixed in later editions.
The Falcon's cockpit is clearly too small to fit the number of people we've been shown it can hold (via the view out the windows seen many times in ANH and ESB). Compare shots of the cockpit as seen in the background of ANH and ESB (especially the scenes of Chewbacca and/or Han on top of the ship repairing it).
The 2004 edition of ROTJ digitally removed Sebastian Shaw's eyes as he plays Anakin in the unmasking scene of ROTJ. Due in part to the restoration process and the removal of the eyebrows the "bald cap wig" that Shaw wears in the scene becomes obvious.
DVD gaffe:
"The Force Fanfare" is drowned out by the X-Wing engines as they approach the Death Star Trench on the English and Spanish audio tracks (and the channels are swapped). LucasFilm describes this as a "creative decision." The phenomena is not found on the French audio track.
DVD gaffe:
All color drained from explosion of Death Star in ANH, with visible blue screen artifacting at the edges of the blast (compare earlier versions and the second Death Star explosion in ROTJ which is orange colored).
DVD gaffe:
The little video clips in the animated menus show various scenes as they were before the Special Edition or 2004 Edition changes (such as Luke training on the falcon with a blue/white saber, and the unmodified sabers in the Luke/Vader duel). Certain other scenes show up properly (such as the 2004 CG Jabba). This is true of ANH on DVD, it may also be true of others.
DVD inconsistency:
On the bonus disc, there is an animated menu showing Luke training on the Falcon (taken from ANH). In the scene Luke has a blue lightsaber, yet in the actual film (2004 edition) it is green in the same shot (and was light blue or white in earlier versions).
DVD inconsistency:
In ROTJ when Luke and Vader's sabers clash in front of the Emperor, Luke's green blade appears to be slightly behind Vader's red blade (or, alternately some have described it as appearing as if each saber is "cutting into" or "entangled" in the other). In previous editions the blade cores were so "white" that they appeared to blend perfectly, and we could assume that Vader had put his blade behind Luke's to block it as the scene logic would lead us to believe.
DVD inconsistency:
Vader's lightsaber changes from red to orange in a few shots in ESB (the "cave vision" on Dagobah, and a brief shot where Vader "leaps" towards Luke on Cloud City). Other color inconsistencies give Vader a red, violet or pink saber throughout the trilogy in different shots. Luke's saber gets a yellow, green, or white core in ROTJ additionally.
Greedo's lines to Han Solo in the cantina in ANH are discernably repeated in the background noise of Jabba's court in ROTJ.
Jawa lines that sound like "Here come da window cleaner" (in english) are repeated several times in ANH (the scene where Threepio is met by Jawas after the sandcrawler "droid hold" is opened up and the scenes where Owen Lars is purchasing the droids). Could be rationalized of coures, but still.
An Ewok says a line that sounds like "Dat guy's wise" (in english) in ROTJ as he remarks to a fellow Ewok while Threepio is speaking off camera.
Jabba's lines are translated for us via subtitles in ROTJ, but the audio he speaks is often repeated (yet translated differently or used in a totally different situation). Could be rationalized.
Won't get into possible continuity gaffes between trilogies or between different movies, or deliberate "easter eggs" of course!
Many more but those are just the ones I remember without looking them up..
