I'm also a laptop carrier. I have to be, since I work for myself and have to transport my computer to client offices with me when I work onsite (which I'm doing more and more lately). I was admiring an Ortlieb Office Bag at a bike shop this afternoon. I almost bought it, then decided to make absolutely sure commuting on my "new" bike agrees with me before I drop the cash. (See, I really can be a practical shopper...sometimes.)

But, I figure with that on one side and a (cheap) collapsible basket on the other, I can bike to the office in the morning, then stop to pick up dinner fixin's on the way home.

Here's the bag I'm talking about:
http://www.ortliebusa.com/cartgenie/...p?pid=36&cid=2

And they also have it in a larger size:
http://www.ortliebusa.com/cartgenie/...p?pid=79&cid=2

I'll also note that they suggest putting the laptop in a sleeve before putting it in the bag for some extra protection.