Little Big Planet.
Halo Reach.
Sony's fine with it, see UT3. However, there is the problem of the PS3 working on a significantly different system architecture compared to the X360 and PC. That's why UT3 maps have to be baked specifically for the PS3.
As for Halo reach... Can you fundamentally alter almost any piece of the game that isn't hardcoded into the executable with it? As has been said many times before, The GECK/CS is not a novelty editor, it is the software development tool that they used to make the game.
Quite simply, Microsoft can control it. They can't control the level of modability that the CS/GECK provides.
Oh yeah, here's another modder tool outside of the CS: http://fose.silverlock.org/ http://nvse.silverlock.org/http://obse.silverlock.org/. Definitely not happening on the 'Box.