i've got an oakley large icon backpack, not sure if a laptop will go in it... but very well built, extremely comfortable to wear and very secure feeling once on. here's a site with it and (do a search of site for "computer backpack") some other items that might help
I've been using a North Face 'Hot Shot' pack and like it a lot. There's a compartment on the inside that holds a laptop in place so it's not flopping around. I've got an IBM T23 which is fairly thin, a thicker laptop or one with a larger screen may not fit in that section though. I think I paid $65 at the local sporting-goods store but I've seen them online since for about half that price.
I have this backpack and like it so much that I don't know why they didn't call it the Bad Ass instead of the Hot Shot.
In fact, tho normally I use it as a backpack, for last weekend's adventures it was stuffed to the hilt and I used it as a tailpack (put the waist strap thru the grab bars to fasten and cinch tight, add a small cargo net for extra reinforcement and it is as sturdy as can be). Versatility - I dig it.
I've been using a North Face 'Hot Shot' pack and like it a lot.
i have a fieldsheer x-pack jacket its built into the coat and can be unzipped too. its a textile coat with great padding,reflectors and comfort. i feel safe in it too. i go to the store ive put a gallon of milk ,baby formula etc.. you dont notice it like a back pac on your shoulders.http://www.fieldsheer.com/products.php?display=x-pack
Whatever you do make sure the backpack has a good waste belt. I have had shoulder straps fail while riding, if they do say goodbye to that laptop. The waste belt will also take the weight off of your shoulders, which is helpfull for long rides. The best design for this is usually small hiking day/day and a half packs.
Another note is to make sure that the opening will stay closed at highway speeds. I had a backpack open up on me on the highway, ever since I make sure the two zippers are down low on the side (they were meeting at the top when it opened). Hope that makes sense....
I was going to suggest the Bobblbee (how do you spell it?). I've saw a buttload of them when I was in NYC. They come in really cool colors (even a "dark" hehe) and are hard. I believe they are designed to cary laptops, PDAs and the like. Check e-bay for good prices on them.
I was looking for a pack as well and stumbled across a review in one of the Brit mags for one made by Kriega. Was highly recommended. Checked out their products online (kriega.com), looked tasty. I especially liked the R35, with it's harnessing and wastebelt, plus a front pouch on your chest for smaller items you may need but don't necessarily want to go digging around in the main compartment, plus good visibility at night. Was a little pricey, but figured, why not. Went ahead and ordered it (through Aerostich.com) along with a separate laptop case they make that fits my PowerBook G4 perfectly. All fit and feel great while riding. Anyway, my 2 cents...