I consider myself to be an expert WinDbg user, when it comes to debugging unmanaged x86 code. I haven't used WinDbg much on managed code, and when I did, I found it quite painful.

Via Scott Guthrie's blog, I discovered Tess Ferrandez's blog. Tess is an escalation engineer in PSS who specializes in ASP.NET and a WinDbg virtuoso. Scott has a list of her best posts. Mind-blowing stuff, but not for the faint of heart.