Threadless!
If you don't know Threadless t-shirts, then - I'm sorry - you've been living in a cave for the last five years. Otherwise, how could you have missed the adoringly artistic and witty internet-age pheonomenon that is Threadless??
Okay, so maybe you don't know Threadless. Sucks for you. But I, being magnanimous, will explain what you've missed:
Threadless makes t-shirts, but they don't design their t-shirts. Nay, they invite you, "the people", to draw or photoshop something and send it in. Then they take those submissions and post them online, letting "the people" (again) to score them.
Once this is done, they take the cream of the cream of the crop and print 'em up. They don't print many, and they usually only print designs once - so when they're gone, they're gone. (There are some exceptions, for the especially awesome.)
It's brilliant. The people-powered design strategy allows for some really amazing artsits and clever graphic designers to get their stunning work produced, and keeps all the styles right on the button of hip. Plus, with the constant input of new designs and the limited runs, they create an awesome "limited edition" feeling - the shirt you're wearing, aside from being beautiful and/or witty as hell, is one of only a tiny number that exist or will ever exist. It's almost one-of-a-kind.
For whatever reason, Threadless designs now have a certain character, making them all identifiably Threadless. What I mean by this is that most shirts are either a) intelligently chuckle-inducing, b) sublime, or c) downright bizarre. Sometimes, they're a combination of all three. The artsists love to play with words (the Community...ahem...party) and they love to play with visual puns and sneaky easter eggs.
I just bought a bunch of shirts. The prices are reasonable ($15-17, hoodies are more expensive). The shirts themselves are quality, and the concept is - have I mentioned it? - brilliant. So, I strongly suggest you head over and peep the catalog for an overload of awesomeness.