As my Exposure has suddenly, mysteriously, stopped working.
Bright enough to see by on unlit roads and with flashy option for dusk in traffic.
shimano hub dynamo + B+M Lumotec IQ Cyo* light is the ultimate commuter light (ignoring the only from Germany £400 dynamo lights).
It does mean rebuilding your front wheel, and did cost something like £140 for the parts but totally worth it - bright enough for unlit roads, no charging hassles, you can run a back light off it too. It doesn't flash, but it is really quite bright, if you really want a flashy light stick on a 10 quid cateye too.
Dynamo is much more convenient than battery, it just stays on the bike, and whenever you need light it is there, the B+M senso ones even turn themselves on automatically when they are needed. It means you don't need to think about lights, like if you decide to go on a long ride after work in summer and get caught out by dusk, or you go out to the pub unexpectedly.
Joe
*I've got the iq fly, which is the older, 2/3 brightness version and it is jolly good - the new cyo must be really quite good
Cateye EL610? Single shot 2W LED .
I have one and it's been very good. Integrated battery and pretty good battery life. High beam, low beam and flash. Got good reviews from the mage too if i recall.
I've even used it offroad paired with a helmet mounted joystick and it was fine.