I would say MagicShine as well. I just ordered one from Geomangear and expect to get it this Friday. They also have a nice rear flasher as well.

I have no connections at all to either company, but from a ton of people talking on the mtbr forums, Geomangear is hard to beat for customer service. Rave reviews. Additionally, dealextreme can take forever to get to you. I don't have experience from either company yet (other than the actual order), but that's how I made my decision on where to buy.

Chris