SnippetCompiler App - a useful application for compiling .NET code snippets, can import VS.NET projects. Has Intellisense and snippets can be exported to RTF or HTML format. Easier than using the command prompt for compiling.
SharpDevelop is a useful Open Source IDE for .NET, so allows you develop without Visual Studio. Unfortunately it is not so good a doing AS.NET projects and is more focused on WinForms development. Currently in Beta 1 status.