Regarding Git, see http://stackoverflow.com/questions/540535/managing-large-binary-files-with-git for a discussion on the subject and also see git-annex.
git-annex does not do version handling for the annexed files, but in all other aspects it works like Git, with pros and cons. Be sure to read what git-annex is not.
I also don't see rsync as an especially bad solution, if scripted nicely. It'll do very efficient transfers. The problem will be if it's hard to define a "master" drive, so to speak. If you only clone drive A to the others, everything is trivial, but if you sometimes add data at drive 2 and want that to propagate to the other disks, it becomes tedious. And what if there are conflicts... This makes solutions such as git-annex very nice. Even if one doesn't get the revision control part of Git, there are many advantages left.
Also, in my experience revisions are seldom (never?) needed for media files and such, unless one is creating music or similar, so the git-annex trade-off is OK in my book.
UPDATE: A good place to find initial information is the Kickstarter campaign that Joey Hess launched to be able to spend much more time on the project. See git-annex assistant: Like DropBox, but with your own cloud.
The rundown of git-annex on lwn.net might also be an interesting read.