JCooney.NET
Richard Grimes Fusion Workshop (yes, that Richard Grimes) Some sample managed GAC API wrappers from Junfeng Zhang Documnetation of the (un-managed) GAC APIs
Dependency WalkerLogging COM Calls by modifying the registry (I've had to modify the registry more in the last week than I've had to do in the last year, not because of COM logging but because of Biztalk and VSIP)
logEnvy is the latest tool I've been working on for searching, sorting and filtering windows and IIS logs, and it's sexy! For more info check it out here.