I haven't played with it at all, but sellsbrothers.com reports:
New OpenGL binding for .NET from the CsGL people, supporting GL 1.1, GLU 1.3, and GLUT 3.7.6. CLS-compliant, cross-platform, yada, yada.
Interesting - the cross-platform support makes it a much more compelling choice than DirectX for people that want to target Mono. It's still in initial release, and I don't think I'll have time to play with it any time soon, but since I cover DirectX on this blog, I thought it was worth a mention.