The GBA Action Replay lets you backup your GBA saves. I don't think it works with normal GB saves though, but I'm not sure.
As I always note when I mention the Action Replay, it is the true GameShark brand. If anything new comes out with the GameShark name, it is the GameShark brand in name only. Datel, the makers of all previous GameShark products, is behind the Action Replay and the Action Replay has always been the same product as the GameShark.
Anyway,"http://www.codejunkies.com" is the website. I'm sure other companies have stuff out there too, but Datel immediately popped to mind.
Edit:
the above is only for PCs running Windows though.