
The venerable Billingham Hadley Small (and Pro for that matter) has a nice cozy spot for the iPad directly behind the padded insert. The iPad sticks up a little bit over the top of the insert, but with the top cover pulled over, it works fine.
If you're looking for a nice compact camera bag that will fit the iPad, the Hadley Small is pretty great.
pics here...
http://leolaksi.wordpress.com/2008/12/11/billingham-hadley-camera-bag-in-black/