I used MonoDevelop to write a WebForms-based ASP.NET 2.0 site last year. It was relatively pleasant, had most of the niceties one would have expected out of Visual Studio. I usually development on a Linux stack, so maybe I'm just not enough of a VS power user, but MonoDevelop was fine for me. :)

SharpDevelop is good for C# development.

It's pretty good for small-medium projects. We currently have a project at ~300kloc and it's painful.