Hey, fellas! I'm back!
My setup is now as follows:
1 20W MR-11 halogen flood.
1 35W MR-16 halogen flood.
1 3-way switch, allowing 20W, 35W or 55W power (both lights together) or "off."
I can run my 20W for over 2 hours, or my 35W for an hour, continuously, using my 4.5 amp battery. I'll save using 55W for trouble spots. My commute is an hour, but only 30 minutes or so in the dark. After the light starts to come, 20W is more than enough to be seen.
And (drumroll, please....)
For $18, I added a 12V car/boat horn w/button ($12 for horn, $6 for button hookup.) This thing is as loud as a car horn, but is only about the size of a small tuna fish can, and even lighter. The button sits directly under my right index finger on the handlebars, so I don't have to move my hands at all to let her rip. (I resisted the temptation to install a "big rig sound" horn. I might be geeky, but I'm not weird!)
(Hey, if you're going to commute to work by bike, you might as well have as much fun as possible!)