I've had luck with a few things -

1. Helmet with good ventilation - I've got a Specialized S Works, which has humungous vents.

2. Coolmax skull cap - helps keep from dripping, also helps keep your head from getting sunburned through the humungous vents metioned above.

3. At last year's end of season clearance on Hammer Nutrition gear, while I was getting the $20 jersey and $30 bibs, I invested another $8 in one of their skull caps. It has a very thin silicone strip around the brim, so it works like one of those sweat gutter things to help keep moisture from dripping down your face. Works really well.