From OP:

- Targus (USB, recommended by enTourage staff, folds: http://www.amazon.com/Targus-PA875U0...4&sr=1-3-spell)

Personal opinion: I bought this keyboard and it's definitely compatible, but I find it cumbersome to fold/unfold/lock. Also, even when unfolded, the keyboard feels like it's about to snap in the middle if you happen to rest it on your knees. Another big gripe is in an inconvenient spacebar and backspace key.

I am looking to buy something a bit more solid and ergonomic but still portable...fortunately reports are that almost any usb keyboard works.