Thanks, guys! Hadn't heard of the Downtube, so I'll check those out.
I commute eight miles each way via public trans. I'm looking for a bike that I can ride in case the trains aren't running, or that I can take with me and have the option of riding home some days. It's all paved in both directions. (Weight is a consideration, I guess, although I know I can't afford the super-light models.)