You'll probably get a Fable II expansion out of Lionhead. The only time they've ever released two full games even close to within a year was Fable to Black & White 2, which still took ~15 months. Given the lengthier dev cycles this gen, you probably won't see another game from them until mid-2010 at the earliest.
The only exclusive you'll get out of Epic will be Gears 3, and it won't be until 2010. Other than that, they're probably working on UE4.
Turn 10 will probably release something this year, as will Rare.
Bungie might announce something this year, but they will certainly only release Halo 3: ODST this year.
As Strategyking said, you'll probably get a few casual titles out of MS, but not much else, outside of something from Rare and Turn 10.
Just look at 2008. Just about every big game released for the 360 in 2008 was known about at least in 2007, and some was far back as 2006 (Fable, Banjo) and 2005 (Lost Odyssey). The only "big" exclusive released last year that was also announced last year was Gears 2.