Microsoft now has a Live Search Club website where you can play casual games for tickets to redeem for prizes. The games include crossword puzzles, word finds, phrase matching games, anagram finding games, and more.
The ticket payouts range from 3 for the easiest game to 25 for Flexicon, which is usually pretty easy but can be challenging at times. It's the one I played to rack up all my points.
Prizes include music downloads, ringtones, headphones, PC and XBox/XBox360 games, XBox360 systems, Zunes, and copies of Vista Ultimate. I went with Vista, since I didn't feel like earning 20000 tickets for a Zune or 35000 for a 360. Getting 6000 for Vista was bad enough.
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After a little fiasco where, as soon as I had racked up enough tickets for it, I found that Vista wasn't on the prize page anymore (as it turns out, they were just out of stock, but chose not to have the prize page reflect that), I now have a copy of Vista on the way. It should be here within 6-8 weeks. I wish it could get here sooner, but I really can't complain since both Vista and the shipping were free.
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EDIT: Oh, and alas, it's for US residents only.