I am doing the thesis's last chapter that focuses on ad formats in video games and hit that part about voice advertising. You know, where a character says "I wish I had a ride like that" and points to GMS Yukon in the latest CSI game. I also remember hearing about Madden doing product plugs in his commentary to the NFL series, but don't have much more than that.
If you know of any other examples, could you please drop me a line (vedrashko at hotmail) or comment below? Any tips or links will be much appreciated, and you will get an honorable mention in the paper. Oh, and I am already writing about fake radio commercials in GTA: San Andreas, so that's covered.
To make this post worth your time, here's a chapter from Game Design Complete published on Gamasutra (free registration) that talks about various kinds of game advertising opportunities. Also, check out my del.icio.us bookmarks on the subject; plenty of goodies there that haven't been posted here.