IBM and are probably the leaders right now. HP is probably not too far behind, although I don't have numbers to tell you if HP is selling more than Sun. But they are definitely one of the top players, and being a large hardware player, you'd probably expect better support.
Of course that is at the device level. If we are looking at the appliances, there are quite a few players. NeoScale and Decru are probably the two largest, but there a number out there that have offerings that may not be as popular.
And when we are talking about software encryption, pretty much all of the mainstream backup products offer encryption capabilities.
Check out the entire Tape Encryption FAQ.
