If you have not already heard of blender check it out it's a powerful 2d/3d graphics tool and it's free.I think it's a great tool for game creation with endless possibilities.
Blender is really powerful once you get to know it. I'm not a pro but here are a couple of things I've made with it just so you have an idea http://andreimaximov.carbonmade.com
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http://andreimaximov.carbonmade.com
https://play.google.com/store/apps/developer?id=Into-It+Games
http://appstore.com/LidiaMaximova