I personal is "in LÖVE" with Unit3D at the moment.
The free version gives you 95% of the paid functionality forever and if you later on decides to go "Pro" its only an upgrade of $1500 for full edition with realtime shadows and loads of shader effects too (bloom etc.)
You will get lights, particle systems, collision, input controls, 3D world, cameras, PHYSICS engine... yes thats right, FOR FREE! Ofcause the paid version does provide you the "extras" but you can easily make great games without the PRO edition.
The game-engine also works cross platform (PC/MAC installs), webplayer plugin (2 mb) mac/pc and if you also pay further you can compile and run the games on iPhone, Android, Xbox, Playstation, Wii ... but go check it out for yourself
I sound like a salesman, but no - I have no connection with Unity3D except that I am currently trying to study and examine how I can build my own games with it as I have tried a lot of frameworks before this, but I must say, its amazingly easy to produce a quick "something" - have no idea how long time it will take me to finish a complete game. But I am on it.