I use a Fenix L2D Premium. The first one I bought lasted 1-day before turning off and on intermittantly (shorting out). I RMA'ed it with Fenix. It took Fenix 2-months and several "reminder" e-mails to get my replacement light... very bad customer service.

As for the light, I couldn't be happier with it. It's actually a bit brighter than my Planet Bike Alias SC 15-watt halogen, but the whitish color of the LED light tends to get washed out more under streetlights.

What I love about the Fenix is I can easily remove it when locking up my bike. I use a twofish lock block. Installation and removal is easy - you just unattach the light with a velcro strap. It's perfect for urban commuting, when it'd be a bad idea to leave the light on the bike.

Battery life is good with NiMH recharageables, and really bad with alkaline. Definately go with rechargeable batteries. They're cheaper, the light will run longer, and they're better for the environment.

I just ordered a new Fenix L2D for my girlfriend. It looks like they changed the LED they were using... used to be the Luxeon Rebel, now it's a Cree Q5. A review on the candlepower forums found that the Q5 is substantially brighter. I look forward to testing the lights side by side. I also ordered the plastic light mount.