I have a Logitech Revue Google TV system in my living room right now and the thing is interesting. It comes with a normal size keyboard that is easy to use and type on. The stock keyboard even has a track pad to control the cursor on the device. The only downside is that the keyboard is hard to store away when you aren't using it.
If you want something smaller that you can type on with your thumbs like you do on a smartphone EFO has the keyboard for you. The little EFO Bluetooth Google TV Keyboard is on sale for about $53 and has an integrated touchpad and QWERTY keys on it. The keyboard has Bluetooth but you can get an RF version if needed and it will work with Linux, Mac, and Windows PCs too.
I have used one of these keyboards before and they are easy enough to use, even if they are much more cramped than a normal keyboard. For occasional typing, the EFO offering would work well enough. The keyboard has 82 keys, supports multiple languages, and has the special keys for the Google TV box.