Main commuter: aluminum hybrid (Rocky Mountain Metropolis) with internally geared Alfine hub. Has kind of a harsh ride, not that comfortable for long distances. I prefer my touring bike (R.M. Sherpa) for longer commutes where I ride to the pool for a swim first. It's so much more comfortable, I'm thinking of leaving the studs on the other bike and retiring it for winter-only use.
I'm always amazed at the sheer variety of bikes that people commute on. I've seen everything from an Electra Townie to a Cervelo time trial bike in the rack at work. Last year a fellow would even show up on a unicycle from time to time. It shows that there is no one perfect commuter bike that suits everyone.