[mcorrell]

An old pair of jeans and a long sleeve T-shirt (or sweat shirt in winter) works for me. What constitutes an old pair of jeans? A good pair that gets an oil stain on them when I forget to change before working! I like long sleeves to protect my arms. I've also started wearing "mechanics" gloves whenever possible. I get cheap ones for oil changes and grease jobs.
I keep a few old beach towels in the garage to protect my cars' interior when working on them so that I don't dirty the seats when climbing in and out.