Jeans, shorts, t-shirts, and polos when I want to look a little nicer. Plain and simple. As for shoes, I've always been a fan of skater shoes, they're comfortable. Right now these are my favorite shoes, comfortable, light, and easy to run in if I have to, not your traditional skate shoe:
http://www.urbanboardshop.com/image.php?type=T&id=529

Levis tend to be pretty decently priced and they're quality stuff, had a few pairs for a long time and I tend to abuse them.

Most people don't care what you wear as long as you don't look bad or are trying to stand out.