Looking for a messenger-style bag

Depends what your commute/desires are. I bike or walk as much as possible, so I went with a more traditional messenger style. I've been using a Timbuk2 freestyle for a couple of years and love mine. They are very comfortable, effectively waterproof, have lots of storage options in a slim profile, and are available in basically endless color options.
The velcro closures can be a little loud (there are two loud velcro pockets to get my ipad out for instance) but I barely even notice any more.

I just bought this one a few days ago: http://www.stash-bags.com/product/11-13-macbook-air-messenger-bag-in-dark-brown-herringbone

Mari is fantastic and accepts to do some light customizations (I asked for a reinforced protection on the back side for the MBA).

You can fit your MBA, some documents and pens, and there are two external pockets for the charger+external hard drive or whatever accessory you might need to transport..

I bought beez reporter bag for my mba 13" and i really like it. Good quality and water resistant
Enough space also for ipad mini and some books