StarDestroyer.Net BBS

I'm making a conference poster and I'm thinking that some sort of rock or sand texture might be good for the background, as it's a porous media related poster. Any suggestions of websites that would have lots of free, tileable textures?

I hate making posters. It's like trying to gets dressed in the morning, only worse.

Here are some links:

Seamless tilable, some with bump and specular map

here some more, also some with bump map

Animax.it - can´t remember if these are seamless