If you're really looking for a new inexpensive light probably one of the newer high power LED flashlights with a helmet mount would be good bang for your buck. Dedicated systems cost more, but have payoff in better light, longer ride times, better quality and easier battery management. Check out the elec/gadget/lighting forum or candlepowerforums.com (here's a link right to the bike section there
http://www.candlepowerforums.com/vb/...splay.php?f=86). Watch out, though, this can be as addicting as biking itself!