4 years to the day after the project was started, SharpDevelop 1.0 was released. SharpDevelop (aka #develop) is a free, opensource IDE (written in C#) for C#, VB.NET, Managed C++ and ILAsm projects.
Features include code completion, WinForms designer (no WebForms designer but that's no big loss since the VS.NET WebForms designer does me more harm than good), VB.NET-to-C# and C#-to-VB.NET converters, VS.NET project import/export, code region folding, integration NUnit Unit Testing, code highlighting, XML Document Preview, NDoc integration, an integrated FXCop-like tool, a regular expression toolkit, and HTML export.
I have played with #develop a few times over the last few years, not every version but at least every 2nd or 3rd version. Each iteration has been a noticeable step forward. The last version I tried was RC1 or RC2 and I had quite a few problems with the more advanced features (VS.NET project import and VB.NET-to-C# conversion) but the main features worked great.
I have not tried #develop 1.0 yet, but will post my results after I've pounded on it for a while.