I know a couple of friends who are waiting to buy a PS3 for FFXIII & God of War 3. One friend who is a die-hard Xbox fan, (he only ever owned Xbox consoles) said he will get a PS3 for God of War 3 and possibly earlier for Resistance 2.
I think Killzone 2, Motorstorm 2, Gran Turismo 5 and Resident Evil 5 will be a strong system sellers as well. Resident Evil has mainly been a Sony franchise aside from the Nintendo GameCube remakes and RE4. Then again with GTAIV MS proved that software sales can be bigger even though GTA was always on Playstation first. It's definitely tough to determine the hardware boost the game actually provided.
As for Little Big Planet it's yet to be proven a system seller but all the hype surely has it at that level. I'm certainly very interested and I plan on buying it.