Platypus Origin 32. I commute daily so I need a bag that can carry everything I'll need for the day, and this one is plenty big enough for that. It also has compression straps to eliminate having a big bulky pack when you're carrying very little. I've had this pack for about 2 years now and it's still in great shape too.

When I want a small pack I go with my REI Stoke 9. Owned it for quite a while now too, and it's holding up great.

Both models are a year or two old now and can be picked up on the cheap.