Dinotte 140L. They go on sale for $100 or so, for the version that takes AA rechargables, if you supply your own charger and batteries.

Seriously, there are cheaper alternatives but they are not in the same class as the dinotte. After my 12V system (with strobe in the back) died, I rode with Planet Bike Superflashes (two of them) for a few months, but as soon as I thought about those lights in fog or rain, I sprung for the Dinotte.