Microsoft CLR Profiler / DevPartner Profiler Community Edition
John Tobler posted "Today, I just had to add a link so you can download the Microsoft CLR Profiler. Two MSDN articles, Writing High-Performance Managed Applications : A Primer and Writing Faster Managed Code: Know What Things Cost, will help you to figure out how to use it. The CLR Profiler is an important tool for tracking down those oh-so-nasty entomological anomalies in your .NET programs."
I'll have to take a peak at this one as well. I've been using CompuWares DevPartner Profiler Community Edition (Free) with pretty good results.