AcademHack suggests that you can use some of the more widely available games, to discuss their cultural significance, representations of race or crime, growth and decline of civilizations and more.
This posting considers what you as an instructor have to think about before teaching using a game; teaching objectives, availability of the game and how difficult the game is. He follows this with a list of critical resources to aid in your teaching.
And of course Second Life is a whole other posting.
It’s been so long since I’ve played computer games (I still have fond memories of Zork I that I have difficulty fathoming how anyone could use gaming in the classroom. Which is where postings like AcademHacks are so useful.