All I can tell you is what I ride for commuting.
I have a Kona Dew (which I'm sure everyone is tired of hearing about by now!) with Speedplay Frog pedals and a Brooks B67 seat. It is (as the LBS described it) based on a cyclocross bike, but with upright bars.
I like it for my commute because it has sturdier tires than a road bike. I am a complete dingbat when I ride, and I routinely run over stuff I shouldn't. It has a HUGE granny gear (34 teeth) to get me through the hills. I've got a rack on it and el cheapo panniers. It's a bit faster than a mtn bike, with a bit more of a road geometry than a hybrid bike. With upright bars I can see around me well and feel like I can "hop" the bike if needed, but I'm starting to feel limited by the bars on my longer fun rides.
It cost $400. If it got stolen while I was in the grocery store, I'd be distraught, but not ruined. It has the same frame as the nicer Konas, but cheaper components. The folks at LBS told me the frame is "bombproof" and I can upgrade parts as needed.
It suits my needs and my commuting terrain and commute riding style.
Edit: oops, I forgot to plug my favorite commuter bike book! The Essential Bicycle Commuter by Trudy E. Bell. I repeatedly check this one out from the library. And I always return it late...
"If Americans want to live the American Dream, they should go to Denmark." - Richard Wilkinson