I'm with prof. Except I wash it once a week (I ride six days a week). I use a product called Phisohex, an antibacterial face wash. And rinse reallyreally well because otherwise if you get sweaty and it any of it runs into your eyes when you're riding it really stings (yes, I've been there.....).

Soap seems to do a good job too though. And really scrub those helmet straps. They get the salt, the sweat, the sunscreen, and the hands with who knows what gribblies on them all touching it. Yuck.

I use a face scrub once or twice a week too, 'cos with all that sunscreen and stuff, and then the dirt you accumulate on a ride (try wiping your face with a clean tissue at the end of a ride and see how grubby it is!) I sometimes need a bit extra to really clean the pores out.