Tom Bihn Monolith
The Tom Bihn Brain Cell is actually designed to 'live' inside a messenger bag. Although they do sell specially made bags to partner with the Brain Cell, you can just throw it inside of whatever bag you have. I've been using their Monolith bag for 5 years now with my PB (the Monolith is like the Brain Cell but is in a vertical orientation to fit inside of backpacks instead of messenger bags).
Here's a link to a pic from their website that shows the inner workings of the bag
http://www.tombihn.com/lapdogdetail.html and here is their description:
Your laptop hangs suspended, cradled in 8mm thick soft foam padding in a 4mm hard corrugated plastic insert that protects from the front, back, and bottom. The sides are protected by dense cross-linked closed-cell polyethylene foam. This offers the toughest protection you can get for your laptop in a case that is still light and minimalist. Just beneath the zipper on the top of the Monolith are two padded flaps. Your laptop will be protected from every angle.
What I like about it is that it is suspended and has the ability to bounce a bit, and therefore I feel like the shock of travel from day to day use is lessened. I have traveled in a dozen countries with my 15" PB in the Monolith inside of an Arc Teryx Arro 22
http://www.arcteryx.com/product.aspx?prod=2830 over the past few years and have never had any problems with day to day use, and my PB still works great and has no scratches (impressive considering I have a scratch prone Titanium PB)
As far as more serious incidents, I did once have my backpack loaded with the Monolith and a heavy text book - and it fell from on a shelf 7 feet up. It landed horizontally (Monolith is designed to protect against vertical oriented shock) essentially sandwiching the computer between the book and the ceramic floor -- and I have since had a small 1 inch white line on the bottom right of my screen, which I assume means the LCD is cracked (it fortunately doesn't actually bother me during use, but it shows that the Monolith is not a Pelican Case or a MacTruck - both of which offer probably a lot more protection, but I don't think they would comfortably fit inside of a messenger bag or backpack.
I'm still a big fan of the monolith, since I prefer to carry my laptop in a backpack. I've just received a 17" monolith to house my MBP I ordered. Only problem is that it's a little too big to fit in my Arc Teryx pack, so I've got to buy a slightly larger backpack. Probably will stick with Arc Teryx, since I don't want a backpack that is only used for a computer. If anybody has any suggestions for backpacks, let me know.
Thanks.