I second the Road Morph. When I first switched to road bikes I tried a crank brothers pump which just about wore me out. After the day of 4 flats I ditched it and bought the Topeak on recommendation of the LBS - also ditched the tires I'd been using.

For a commuter, where you need things to be reliable and always available, I consider a good pump to be irreplaceable. CO2 would only be acceptable to me if my ride were fairly short (no ability to accurately control tire pressure) and I had decided to carry more cartridges than I thought I needed.