Small (8-10 litre) capacity messenger style bag?

Any suggestions on a good and small messenger or "briefcase" styled bag?

It really should have a capacity of no more than 8-10 litres in size, as the typical occupancy of the bag will be in the 4-6 litre range.

Not looking to spend a large amount on this little guy, though I would very much place importance on durability and ease of accessibility over any appearance or material concerns.