Lots of possible styles for a good coommuter, but it should have clearance for tyres of appropriate size (usually mid-size slicks) and fenders, luggage capaciity (usually a frame-fitting rack), a number and range of gears suitable for the rider, load and terrain (hub, derailleur or single/fixed). It should also be a light as possible without being fragile.
Most good commuter bikes occupy the middle ground in termms of design parameters, an area badfly served by the bike industry.

I agree with Dahon Steve that hub-gears could be far more widely used for commuting duty, but the Dutch and Chinese seem to use them on the heaviest most cumberson grade of bikes. This, I think, is wh
at gives hub gears a bad rep.