The 7D with 400 f5.6 is a good combination. I don't find that a lack of IS is too much of an issue, if you are shooting from a hide I use a tripod, down to 1/250 I can get sharp shots with a tripod. Your limited by the quick movement of the birds anyways so often need a higher shutter speed to freeze movement. Shooting handheld with a slow or stationary subject it where you'll find the benefit of IS.
Have a look at my Birds set of Flickr to see the results of this combination. http://www.flickr.com/photos/eimajm/sets/72157624573654777/
If you really want IS 100-400 is a popular lens, and good for general wildlife/nature due to the zoom, but more expensive that the 400 bare.
Have fun with whatever you decide.