Honestly, I've been really impressed with what Bell has been marketing at Walmart etc. for ten bucks -- this one. It's very bright and the circuitry is quite durable (I've been using them for about four years and they've survived many knocks and falls). Much better than your average cheapie and outperforms many LBS lights I've owned. My only complaint has been that the plastic clip on the back has broken -- but that's only an issue if you're going to clip it onto yourself or the bike, rather than using a bracket.

OTOH, if money's not a concern, people swear by the Dinotte. Haven't tried it, myself.