GigaOm has confirmed the ad buy by the Obama campaign in Burnout: Paradise, an Xbox Live racing game. (Update: AP says there are nine EA games in the buy, including Madden 09.)
Also, check out Pork Invaders, McCain campaign's advergame on Facebook and a clone of a GOP game "Tax Invaders" from the 2004 cycle, which, of course, itself was a clone of an 80s arcade blockbuster. Here's some NYT's background on political advergaming. (Shoot some pork with embeddable version of the game below).
(keywords: political advergame, political in-game advertising)