Well, I thought I'd tell you guys about 2 sites I know of, that you mightn't know of, these are gigposters.com and drawn.ca

Gigposters is used mostly by professional poster artists, has some very nice poster designs, some even for sale. One of my favourite artists (Guy Burwell) has submitted work onto the site as well

Drawn! Is a blog that makes posts about artists and their art, I've seen some great websites thanks to these links (One of which is a blog of the great John K., the dude who created Ren and Stimpy).

So do yourself a favour and check these sites out.