The only one I have experience with and really like is the OGRE 3D engine. Granted it's not a game engine but it has been used in games, demos, and many others.
Here's a direct quote from their website:
OGRE v1.2 [Dagon] represents the culmination of 5 years of continuous development, resulting in what is now regarded by many as the leading open source real time 3D rendering engine. OGRE is packed with features to make your development life easier, whether you're making games, architectural visualisation, simulations, or anything else which requires a top-notch 3D rendering solution. See what others are saying about it, and download your copy for free today!
You can check it out at www.ogre3d.org
Also, I co-authored a paper on this topic that you can get to here: http://www3.intel.com/cd/ids/developer/asmo-na/eng/254761.htm?page=1
