Ogre is the best Graphic Engine available for free. Ogre doesn't cover all field a game engine should do. Ogre doesn't handle physics, networking, AI, audio...
If you want to collect a good set of free libraries I suggest you to use
- OGRE for graphics
- Bullets (or ODE) for physics
- Raknet for Networking and MatchMaking
- "something else" for audio and AI
If you need something powerfull (but expensive) I suggest you C4 Engine (350$) or Torque (150$).
