SlimTune is a free profiler and performance analysis/tuning tool for .NET based applications, including C#, VB.NET, and more. It provides many powerful features, such as remote profiling, real time results, multiple plugin-based visualizations, and much more. The source code is available under the terms of the MIT License.
Go to http://code.google.com/p/slimtune/
See also these related projects.