Originally Posted by nizwiz
Another option would be to look into Crystal Space / CEL (check out the demo release of Crytal Core, it doesn't look bad at all). A big pro is you can use blender to create assets for it.
But idtech 4 would certainly be the best choice, if you can wait.
I've also looked at CEL and Crystal Space. As of right now, they don't have an engine or any SDK so all it would give me is more code to play with. Although that thing about using blender did catch my eye.