Since you ride with him, has he ever mentioned what he wishes he had, or have you noticed anything missing?

For commuting, lights, PB Super Flash if you can find a sale. I really like the Crank Brothers speed levers for easier tire changing, Incredibells, velcro pants clips if he ever has to ride in street clothes, helmet mirror, beanie, or doo-rag. If there's a bike store in the area he likes, a gift certificate is a bit lame but lets him get what he wants. We had a gift exchange at work today (with swapping) and the big hits were a bottle of wine and several Starbucks gift cards. I was tempted to bring something cycling-related, but I'm the only regular bike commuter in the group.