ThereIn terms of game engines:
- Torque3D: Lots of features, but some would consider the code difficult to work with.
- C4 Engine: Inexpensive, excellent author support, but the tools could use a bit of work.
- DIY: Select a set of libraries and glue them together with your game.
Since Ogre3D was suggested, there also exists a light-weight alternative to Ogre3D, Horde3D.
Pros:
- The design is sound and will likely outperform Ogre3D for heavy rendering (if it doesn't already)
- C API, making bindings for languages like Python simple and easy to maintain (internal code is C++)
Cons:
- Requires at least OpenGL 2.0 support
- Smaller community
- Unstable code base (major architectural changes are still occurring)