(Jeko) Quickgraph: http://www.codeplex.com/quickgraph
(Jeko) NPack: http://www.codeplex.com/NPack (Jeko) Others: http://www.codeplex.com/NPack/Wiki/View.aspx?title=What%20are%20the%20Alternatives%3f&referringTitle=Home (Jeko) dnAnalytics:  (Jeko) http://www.nuclex.org/weblinks/Programming/Math
Found a .Net wrapper! http://code.google.com/p/opencvdotnet/
Intel's code written in C++ in 1999-2000. Not too much going on with it, but it was used by Stanford in the Darpa Grand Challenge. It has code that should be thrown away, but it is comprehensive. I think we should start with it, especially that there is a .Net wrapper
Motion Strategy Library, http://msl.cs.uiuc.edu/msl/
Motion Planning Kit, http://ai.stanford.edu/~mitul/mpk
Darpa contestant (will try to get the code) http://www.torctech.com/services/software.html
Urban driving simulator http://portal.acm.org/citation.cfm?id=1296777
Ogre: http://www.ogre3d.org/ A good and popular one with a big online community. Used by many "serious" project, it is well documented. A friend of mine worked with and recommended it.
http://www.ogre3d.org/wiki/index.php/OgreDotNet (Supports mono, not that used)
http://www.ogre3d.org/wiki/index.php/MOGRE (Popular, doesn't support Mono)
I've been using openscenegraph for 2 years (that was 2 years ago) and it has been a pain! Lack of documentation and a few bugs. However it is quite popular, it is still not very mature. Its good points however: there are many import of 3D formats supported and it offer good real-time performances.
(Jeko) More: http://www.freeprogrammingresources.com/gamelib.html
http://www.racer.nl/, nice looking, source code available but not open source (restrictive license).
http://www.ultimatestunts.nl/, require art work to look better. The track format supports junctions.
AForge AI Library written in C# Image processing, neural networks, machine learning, and vision. There is a decent amount of traffic on the forums, and the releases have thousands of downloads. The guy is from Latvia and has linked-in profile says he is looking for consulting work: http://www.linkedin.com/pub/4/410/A72
Article about library: http://www.codeproject.com/KB/recipes/aforge.aspx?display=Print
Removed from consideration
All in C#, but going through a rewrite, and they don't have a community yet.
Delta 3-D http://www.delta3d.org/
PLIB, Portable game library: http://plib.sourceforge.net/whats_inside.html Features: sound effects, music, a complete 3D engine, font rendering, a simple Windowing library, a game scripting language, a GUI, networking, 3D math library and a collection of handy utility functions. Each library component is fairly independent of the others - so if you want to use SDL, GTK, GLUT, or FLTK instead of PLIB's 'PW' windowing library, you can.
This is a cool component for people making simple games, but we don't need most of it, and the stuff we do need isn't that powerful or popular. Torcs uses it, but that will change :-)
Irrlicht: http://irrlicht.sourceforge.net/, also has .Net bindings
Looks like a good engine, but some have complaints about it: it is less pluggable, less powerful, etc.
http://axiomengine.sourceforge.net/wiki/index.php/Main_Page This is a port of Ogre that is clean, rich, and supports Mono. It doesn't have the community of Ogre and Irrlicht. Using a native C# component is awesome, but using something with a community is more important.