I carry my laptop to work in an Arkel commuter pannier. The Arkel pannier has a padded compartment for the laptop, and a separate compartment for clothes. It allows me to carry everything I need for the day in one bag.

I am still undecided on whether I would recommend this pannier to other people. It does carry everything I need, and it all fits in one bag so I have less to load and unload (I like getting the commute down to as few pieces of gear as possible).

However, it is pricey and very long...even though I commute on a touring bike (Trek 520) with long chainstays I still have some trouble with heelstrike.