Here. From Matthew Mastracci: I just released the fifth alpha version of my free, open-source .NET profiling application. It supports everything I've thrown at it so far (multi-threaded programs, NAnt, SWF apps) and is getting close to feature-complete.
It comes with a basic VS.NET add-in that lets you profile from DevStudio. There is a complete source package on the downloads page for those who are interested in learning how a profiler works, or just want to tinker.