Plus one on Magic Shine, but NiteRider makes some awesome lights as well. Just do a Google Search on those Madd mentioned along with NiteRider. Online outlets like places like USAJenson, Pricepoint, Universal Cycles, REI, among a few others will have them and some times on sale at a great price.
"I am what I am, and I love gravity riding! Wherever I can Roll On and Over Gnarly Dirt, Fast DH Runs, Huck Big, AM, or the Urban Jungle (street), I am having fun."