Blanka is a collection of original, vintage, and limited edition posters and prints.
Rumplo will help you waste even more of your hard-earned cash on artist and designer created T-Shirts. You can submit shirts you've found anywhere online, as well as comment on and favorite other people's findings. Thanks to user-submitted tags, you can browse by color, type ('boys', 'girls', 'kids'), and many other attributes. If you get bored of browsing aimlessly, you can always check out what's popular.
Pixeltees - use a (shockwave) editor to produce t-shirt designs. The low resolution, restricted palette and video-game connotations give interesting restrictions - a lot of designs are terrible, but some are pretty neat.
Design is kinky tshirt comp is pretty cool.... these guys seem to be always trying to do something for the visitor rather than just spouting about how good a designer they are like most design related sites. Makes a nice change!