Thanks all for the suggestions. To clarify the above questions:

1) I'd probably like to keep a good solution under $150. I was considering building a dynamo wheel, but it would be more like $200 when all is said and done.
2) Part of the reason I think the dynamo is unnecessary is that I'm commuting 10 miles each way on almost entirely well-lit city streets. Lots of accidents are from "doorings", though, and this is the sort of catastrophe I am hoping a sufficiently bright light will help me avoid.
3) I don't have a run-time requirement, but I think ideally I would like to get a work week out of it, so, 40 min each way x 5 days.

I have had quite a few lights in the past, and the ones that aren't advertised as waterproof have always ended up shorting out due to water in the battery compartment before long. I ride in absolutely all sorts of weather, and don't get off the bike in rain unless it's blowing so hard I can't stay upright.