Seems eagles fly upside down as well!

[AndyJWest]

It looks to me like he's doing a split-S: rolling inverted into a half-loop. I doubt if eagles are capable of sustained negative-G flight - the wing muscle development would be all wrong, and the extreme camber of the wings wouldn't help. Nice photo though.

Edit: A nice photo of a Red Kite doing an impression of a Stuka - http://www.flickr.com/photos/geoff-e/3925938345/

[Catseye]

They can, including other birds such as Canada geese.
However, look at the head - regardless of the plane of flight the bird is on, the head is always oriented to the ground in a normal position. Built in gyro system. Without maintaining sight in the standard horizontal axis the bird becomes disoriented.

This bird is in effect doing a split ess. The legs are extended acting as airbrakes to facilitate the immediate dive, the tail feathers are bent as in a set of elevators, the eagles left wingtip feathers are pulled in facilitate a push for a bit of sidewards roll air resistance as the bird rolls to its right. I'm willing to bet that in another millisecond the right wing would pull right in to complete the roll and then both wings pull in for the georgeous eagle controlled dive. Also, the neck is rotated in such a way as to facilitate the right direction roll. Incredible utilization of natural gifts. This shot reminds me of a dive bomber doing a 270 with eyes-on target.

Marvelous things birds.
It's great being an amateur birder.