mrstickball on 11 July 2008
Texas Hold'Em, Carcassonne and Undertow have been free at one point or another to the entire market.
Texas Hold'Em: Free the first 2 days it debuted (Aug 2006)
Carcassonne: Live is 5ive (November 2007)
Undertow: XBL Downtime Apology (January 2008)
Back from the dead, I'm afraid.