For the last three weeks I've been riding my bike to work when occasion permits. Unfortunately, that usually only works out to a few times per week. I live in Lindon and work at Thanksgiving Point, about 17 miles one way. One of the first things I discovered was that I needed a good way to carry my laptop.
I have a backpack and a messenger bag. I immediately dispensed with the backpack since it's up high and made me too hot. The messenger bag keeps the weight low, but after 17 miles, it's a boat anchor around you neck.
What I needed was a pannier big enough to carry a laptop. I used to commute by bike regularly but that was 15 years ago. My panniers from that time are small and not nearly big or sturdy enough to carry a 15 inch Macbook Pro.
After a week or so of searching and reading message boards I came across the Arkel Commuter. This is, as far as can tell, the best commuter pannier around.
At $159, it's not cheap, but after using it a few times, I think it's well worth it. The load is low and the bike is doing the work. The bag is well made and the laptop is secure. I especially like the cams that lock it to the rack--the last thing I need is my laptop flying off the bike on a bump.