The lists I've seen are pretty complete, however I'd toss in these items.

Sharpie pen (velcroed to the stem) for writing down license plate numbers as needed.
Conspicuity tape ($7USD) to add reflective touches to the bike (as well as several friends' bikes).
Lightweights for wheels, to add reflective touches to the bike (watch this looping video)
Camera for documenting the good and the bad you see on your way.
Good rain gear, riding in the rain can be fun, but being cold and wet sucks.
Cell Phone in the event of an emergency.
Bike ID kit, being ripped off sucks. ID kits can help deter thieves, and get your ride back if it's stolen.
A bike computer for fun (and you can join us on the The 2011 Commuting Mileage Thread)