I use a Timbuk2 laptop back pack when I commute. I do have a pannier for my clothing and toiletries, but when I have to take my laptop, I also use this backpack. It's quite comfortable. My commuter is set up the same as my road bike (same aero position), so I'm sure this would work as well if I were on my road bike, too. It's small enough to not get in the way, but large enough to hold my laptop and other stuff as necessary. It's also got a small channel that runs the lenght of my back (from head to butt) that allows air to flow underneath it. If I tip my head down for a second or two, the air flows right in and cools off nicely. It's really a smart design and a great backpack.

In fact, just yesterday I was thinking about how this backpack has been through a LOT and it is holding up beautifully. I use it as my carry-on when I fly, too...because it can really hold a lot and it protects my laptop very well.

This is a similiar one - but mine has one less compartment, so it's a little sleeker. I don't see in on Timbuk2's website though. I got mine through SAC for like $40, too.

http://www.timbuk2.com/tb2/products/...track-day-pack