I walk to work, and as such a good laptop back is a critical part of my commute. For the last few years I've used an L.L. Bean messenger bag, but it had become frayed and ink-stained from years of abuse. It's form factor was also problematic, particularly when I fly, because it was difficult to stow under seats while still giving easy access to its contents. I also wanted easily stow cables, notebooks, pens, and other tools of the my trade. Oh, and a laptop as well.
After a surprisingly little amount of searching I've found my new bag: L.L. Bean's Quad Backpack. It's a comfortable, laptop-friendly backpack with three large compartments: a zipped and padded one for the laptop, second, somewhat smaller zipped one that sits in front of the first, and then a flip-top compartment with no zipper. There are a number of smaller side compartments as well.
It retails for $79.95, but my wife was able to pick it up at the L.L. Bean Outlet store for $30 because it was a return that had already been monogrammed. This led to lots of questions about what the initials stood for, but we were able to eliminate those by sewing a NASA meatball patch over it. The patch complements the red bag nicely; it looks like it was there from the beginning.
I love it. I use the front-most compartment to hold my myriad of cables (Lightning-to-Firewire, Lightning-to-Ethernet, DVI-to-Mini-DVI, VGA-to-Mini-VGA, iPhone cable, etc.), which are in turn packed in a heavy quart ziplock bag. This was a brilliant move because it keeps them from becoming a synthetic snake ball at the bottom of my backpack. I also keep my IronPigs hand towel in there because hey, you always need to know where your towel is. What I love about this compartment is that it buckles, rather than zips, shut, so it's really easy to get to during meetings. The top-most zippered compartment sports the NASA patch and a gaggle of pens, pencils, and other assorted writing utensils.
The main body of the backpack contains a laptop sleeve. It fits a 15" laptop snuggly; my 13" MacBook Pro Retina is a little loose, but not overly so. I have both (15" at work, 13" at home) and it works well either way.
The two other compartments are given over to books, my iPad, and my lunchtime gaming supplies (e.g. Savage Worlds Explorers Edition Deluxe, Dragon Age ... I tried the Numenera core book but it was too damn heavy).
It's a comfortable backpack -- it has a chest and waist harness so I can pretend I take it hiking, but I don't use either. It's comfortable as is, and easy to adjust when I swap out my light jacket for my winter ski jacket. More importantly, it's slim -- my previous laptop backpack was so bulky that I'd knock into people when I took it to conferences. I road-tested the backpack at HighEdWeb Buffalo in 2013 and had none of those problems.
I haven't taken it on the plane yet, but I expect it will easily fit under the seat. This was a big issue on my last trip to Portland with the messenger bag: it fit easily enough under the seat, but it was a pain to get things out of.
Of course I use it for more than work. I've got a old orange backpack that I've been taking to conventions for years. It's now officially retired in favor of the new backpack. All the compartments work great for separating out rulebooks, gaming supplies, dice, etc., at least for my regular Pathfinder game.
All-in-all, it's an excellent backpack and well worth checking out if you're in the market for a new one.