I like to use a touring bike. The Trek 520 is sturdy, tires arn't too wide, and it's comfortable. With paniers I can cary anything that I might need at work, plus there is room for groceries, if I have to stop on the way home. I know that my bike is out of your price range, but you could get something like it. Some people also like the bikes that are set up for commuting, and they tend to be less expensive. If you have cobblestones or lots of pot holes, you should have the wider tires and maybe suspension.

If you become carfree, of course, price will be no object.