http://www.roadandtrack.com/article....rticle_id=6814
Based on that road and track article I'd guess there will be:
LS - 3.5L pushrod V6 220HP
LT - 3.6L DI V6 300+ HP
SS - 6.2-liter LS3 V-8 400HP
Z28 (a year later) - super-charged 6.2-liter sibling to the Corvette ZR1's LS9 motor known as the LSA 480-500 HP
And maybe replace the base V6 with a 260-bhp turbocharged 2.0-liter four in the 2011-2012 timeframe for gas mileage reasons.
Dunno how accurate you'd consider Road and Track to be, but that's what they think at least.