Timbuk2 Classic Messenger Bag

Business enough that I use one as a brief case, and tough enough that one is my commuter bag. Rugged and spacious, comfortable and practical.

This bag is perfect for school, work and basic all around needs. It holds my computer and my books with some room left over to hold my lunch. The should pad is definitely needed otherwise I would have an indentation on my should where the strap was.

This bag is outstanding, there is a reason they are so ubiquitous. Sizing is pretty large, I got the medium and can't imagine being able to carry the bigger ones on my bike. The medium fits my 15" laptop in sleeve, my change of clothes/shoes and my lunch pretty handily. You can squeeze more in, but may sacrifice the water resistance. The inside pockets handle all my tools, tubes, and toiletries as well.
The bag does everything it advertises, I got caught in a downpour with this on and was completely soaked, but everything in the bag remained dry. The cross strap works well to secure the bag and keeps it from shifting around while I ride. Also there is some flexibility so I can change the position of the bag slightly as I get tired.
It works great off the bike as well, which is great if I am stuck driving or taking the bus. Looks good and performs well. I got this at a great price on BonkTown, but knowing now how great it is I would have paid full price.

If there's someone out there that hasn't owned one of these bags, I'd be surprised!
Unless you're one of the fixie guys or gals that needs to separate yourself visually from the rest of the pack, any rider will find this bag functional, and big on storage nooks and crannies.

Pros: Lots of independent storage areas for small items.

Cons: all storage areas are on the front side of the bag. If the bag is relatively empty this leads to the front folding in against your back.

Also, if you ever carry two items that don't mix (gym clothes and magazines or papers, for example), I highly recommend you look into the laptop version of this bag. The laptop sleeve provides storage for paper items and keeps them from getting torn up and bent.