Most of the time it's cargo shorts, flip-flops, and a t-shirt that's has either a band, cartoon, or witty or sarcastic saying on it. In the winter the shorts change to jeans and the shoes to knock-off Chuck Taylors (I can't see spending $40 a pop on the real thing when I can buy the $10 ones at Walmart and they last about as long). When I have to look decent replace the T-shirt with a button down shirt of some kind.
I get most of my button down shirts from thrift stores. T-shirts come from here: http://www.thinkgeek.com. Kohl's has some decent stuff every once in a while.