I was recently kindly sent a copy of Portem from Mirrow Games, which is a very rare thing: A free roaming 3D game with a one-switch mode. Rarer still is the "Brain Fingers" mode allowing for brain/face muscle control. See my full review over at the Accessible GameBase.
A few more one-switch games have come my way recently too, that you may like to investigate. In rough order of ease of play: The Cow Jumps Over the Moon and Jack Be Nimble (via TLWMSN Blog); Mine Sweeper-esque Bounty Sweeper and Tron like Trail Blazer; The Flood Runner 2 (via Accessible GameBase).
I must make time too for Graeme Singh's fantastic utility that can make emulated fighting games, such as Tekken and Virtua Fighter one-switch playable.