I never have to look at the buttons when using a numeric keypad, and the '5' key is usually dimpled so you can tell where you are by touch. But I know what you mean about game controllers having well delineated button placement.
A Wiimote would probably work really well, uses bluetooth, is designed to fit in the hand and had well defined button placement, as you can see here:
http://www.wiiprojects.org/Bluetooth/WiiMote.gif
http://www.youtube.com/watch?v=PnmkygmGNiM