I'm currently using the CryEngine for my own project, the sandbox editor is pretty sweet and my favorite world editor next to torque3d's editor.
You can download the SDK and it's tools here.http://www.crydev.net/
If you can afford it I would highly suggest investing in the autodesk suite, it has some pretty insane tools. 3ds/maya + mudbox = awesomeness! You can also get it by other means but it's a no no in anyone's book,
CryEngine uses the lua programming language, lua is pretty simple to learn so it shouldn't take you long before you make something pretty cool!