Model M Keyboards
The old and the new: I'm typing this on a Unicomp Model M (modern construction of the classic IBM/Lexmark keyboard) hooked through the Camera adapter (ie. "the USB port that should have been there all along") on my iPad. I did get a "The attached USB device is not supported" message, but that's because this particular Model M is the version with the ThinkPad-style trackstick, which shows up as a normal mouse; the keyboard itself is working fine.
If the camera adapters weren't (a) so expensive (b) so scarce and backordered, I'd just leave one with the keyboard...