I can't believe no one has done this already, but I'll list when Xbox 360 exclusives were announced and when they were released (I did do this is the English version of dates so it goes Day/Month/Year FYI)
First Party
Halo 3: annonced 05/09/2006, released 25/09/2007
Halo ODST: announced 02/06/2009, released 25/09/2009
Halo Wars: announced 27/09/2006, released 26/02/2009
Banho Kazooie: Nuts & Bolts: announced 13/05/2008, released 11/11/2008
Fable 2: announced 05/09/2006 or 09/05/2006 (I don't know which one here :/), released 21/10/2008
Fable 3: announced 19/08/2009, released 26/10/2010
Forza 2: announced 27/07/2006, released 10/05/2007
Forza 3: announced 02/06/2009, released 27/10/2009
Second Party
Blue Dragon: announced 10/05/2006, released in Japan 07/12/2006, released in America 28/08/2007
Lost Odyssey: announced 23/09/2006 (this is a rough date as I narrowed it to TGS 06, but can't find an exact date), released in Japan: 06/12/2007, released in America 12/02/2008
Crackdown: announced 04/10/2005, released 20/02/2007
Crackdown 2: announced 01/06/2009, released 06/07/2010
Gears Of War: announced 18/05/2005, released 07/11/2006
Gears Of War 2: announced 20/02/2008, released 07/11/2008
Gears Of War 3: announced 13/04/2010, release date 20/09/2011
Halo Reach: announced 02/06/2009, released 14/09/2010 (I think Bungie was independent at this point)
Mass Effect: announced 04/10/2005, released 20/11/2007
Third Party
Mass Effect 2: announced 17/03/2009, released 26/01/2010 (it was exclusive)
Splinter Cell Conviction: announced 06/01/2009 or 01/06/2009 (again I'm not totally sure), released 13/04/2010
ok thats quite a few games and this took me nearly an hour so I'll stop there, if you want add any games feel free to make it more complete,
