I'm commuting in the Boston suburbs, as well, on a hybrid bike. I really like my bike for my commute, but if I had to buy a new one I'd probably look at a road bike and get some solid puncture-resistant tires. I've been keeping an eye on the Boston C-list lately and I know that you could find a good commuter bike for under $400. There are plenty of people dumping their not-too-old bikes when they upgrade to the latest and greatest.