Torque Game Engine (3D) by Garage Games
Torque Game Builder (2D) by Garage Games
PopCap Framework (PC only?)
PTK Game Engine
Would anyone be interested in coming over to our house some weekend and having a mini game jam to try out one or more of these engines? Maybe one a month? Get the 30 day demo, grab some free art, and see what you can really do... I think it would be fun.