SnippetCompiler is another useful tool for C# developers. Is quite similar to FastSharp. Both allow you to write and compile sample code very quickly. SnippetCompiler has IntelliSense support (missing in Fast Sharp), that gives benefits. Unfortunately, last version is from year 2008… supports .NET up to 3.5….
There are always pros and cons when a tool provides something extra (IntelliSense here) and miss something else (.NET 4.0). I personally use SnippetCompiler to test sample code.