Torque Game Engine (3D) by Garage Games
Torque Game Builder (2D) by Garage Games
Unity (3D/2D)
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.