Over the past few weeks Tess Ferrnandez, an escalation engineer at Microsoft, has been releasing the first of her 10 part series of labs advanced ASP.NET debugging. At the time of writing there are three labs covering Hangs (deadlocks), Crashes, and Memory Leaks.
I really can't recommend these labs enough. Not only do they take you through step by step on how to look at the problems, but each lab asks you questions (eg. "What thread owns the lock?") that are later answered in a review post.
Absolutely top notch quality so far and I am really looking forward to the rest of the series.