I use this guy. It's quite small. For a size reference, it for my 13 inch MacBook Pro, and a couple pens, a wallet and that's about it. So maybe that will be a perfect size for you. It's also cheap.

I haven't used it in a while because I've been using my Timbuk2. If you live around the same area as me I would totally let you try it for some time. I'm in the Bay Area.