I use what is basically one of those outrageously expensive, miracle fiber backpacking towels, but found some at a dollar store for... a dollar.
They don't come in fancy colors or have a grommet in the corner for hanging, but so what? I can do that myself if needed. These babies suck up water like nobody's business and dry
fast. I should add that I got the idea of looking for them in the dollar stores from Hoodoo.
Edit:
Forgot to say that if you can't find the el cheapos like Hoodoo and I, try the auto stores. Around here, you can buy an artificial chamois cheaper than the fancy BP towels (same thing, BTW).