Create your own games and put them to the test with these awesome resources. Introduce students and inspire creativity for them to not be on the receiving end of cool games but on the offering end. So often we take in but let's start encouraging our kids to be the developer and not just an "end user". You may want to dapper in to one of these resources first, spark their creative problem solving skills and then introduce the software to the students...and let their imagination "run wild".
And here are a few more to check out:
Panda 3D - FREE
RPG maker has a free trial.