Gamasutra has an interesting game design article on making your video game accessible to those that have disabilities. It talks about the motivations behind creating games that are usable, which tend to have design elements that make them accessible to various disabilities. Game design challenges are looked at and how they may conflict with one gamer over another. There is a section on creating simple game control schemes that allow the game developer to open the game to a wider audience. Lastly, it discusses the critical step of testing the game with target groups of gamers.