I picked up an Eagle Creek Travel Bug Daypack last night at REI for $50. It fits my iPad in its Marware Ecovue Case, my Apple wireless bt kb (inside a Waterfield designs slip case), and a few other small items (iPhone/wallet/etc) quite nicely.
Also, the Timbuk 2 Freestyle Pro Messenger XS fit all of it nicely too, and was more padded. But in the end I went for the Eagle Creek because of its small profile and backpack straps so I can sling over one or both shoulders on the go. I'm currently using it as my everyday bag, and then tossing in the Apple keyboard when I know I'm going to use it for writing or blogging.
http://www.rei.com/product/773423 (does not come with goofy water bottle that's in the picture in the side pocket)
If you're a girl, the Sherpani Flora Minor Messenger bag is also a perfect fit, with a little more room but less organizer pockets. I'll have to save that one for a rainy day buy.
http://www.rei.com/product/797097