I swear by Dickies pants. They are terrible until you get about 50 washings in them. Once they are worn in, they are comfortable as can be and they don't hold a lot of stains. A bonus is they are cheap!
I usually throw on my boots and I have some old plain white t-shirts that are specific for the garage. I am going to invest in some good coveralls one day. My last pair didn't last long, so I just never bought a new pair.
Ed
Old jeans, old T shirts and old truly crappy athletic shoes.

I like these for working
http://www.armedworkwear.com/products/khaki-work-pants/
Built in knee pads are nice also.




