Sony's PS3-only racing game was announced in 2006, but was expected as far back as Gran Turismo 4's release in 2005. Since GT4, three Forza racing games have come out on rival platform Xbox 360. No Gran Turismo console games. (A long-missing Gran Turismo PSP did finally come out in 2009, though)
The game has been playable at Sony events since last year, which is more than can be said about most of the other games on this list. But, screeching around the bend for an early to mid 2010 release, Gran Turismo was just shifted to a TBA release window by Sony.