I just came across this review of the CoolMac Flexible, Waterproof keyboard.

It looks pretty nifty: lightweight, low profile, sealed, full-size keys. No Keypad though.

The review indicates that it's made to use with Macs, but it might also be compatible with Windows machines. If not, there's probably something equivalent -- or there will be eventually.

I wonder about durability, since it can be rolled. Seems like the wiring could break down after a while.

If they came out with one that was Bluetooth compatible and had a keypad, I'd consider giving it a home in my laptop bag.