Enter the iKeyboard. In fact, I'm typing this article using one! The iKeyboard is an overlay for the iPad's built in virtual keyboard, in landscape mode. It stays in place using a sticky backing yet it can be applied and removed repeatedly with no residue.
The iKeyboard is essentially a plastic frame with clear rounded 'domes' above each key. When you touch the key, there is a physical response and you can hear the click as well, so touch typing is possible. And unlike a Bluetooth keyboard, autocomplete still works, so you might be able to type faster!
The iKeyboard is thin enough that you can close the Apple Smart Cover without removing it. The iKeyboard is available in white or black and currently supports the default US English keyboard, but more keyboard formats might be available in the future. See www.iKeyboard.com for more info.