There are alot of options out there for light use/commuter use. Some good suggestions have been mentioned already. I'm a big fan of NiteRider. Their products are outstanding. I've been running the same light set with the same two batteries in 24 hour races since 2001 or 2002. Never a failure - I'm even on the original bulb (yes, I have a spare). Bought another NiteRider this winter. These are the high end lights that put out enough candlepower to take xrays. When I ride at night on the road, I am often mistaken for a motorcycle. A really quiet one.
But I also picked up a little USB rechargeable NiteRider light for my handle bars. I intended to use it just as a backup light in case my primary failed in a race. That said, it's become my favorite light for general uses. The claming system is robust enough for off-road racing, get about 5 hours of light from it depending on the setting, and even the low setting is surprisingly bright. They are the Lumina series. I've seen them new from about $80 and up (brighter/longer batter = more $$$).
This light is just fine for most commuting, even some night trail riding if you aren't going fast. With the USB recharge, you can charge it anywhere and it's also small. Great little light. PLus, when you buy NiteRider, you are supporting those who support the sport (24 hour bike racing).
angela (throwing downing shameless plug for her favorite lights)
angela