Wintellect ASP.NET FAQ
Nothing beats a well constructed FAQ based on lots of real-world questions. It's a little old, but I was surprised how much genuinely insightful material is present in the Wintellect ASP.NET FAQ.
It's a mixture of the mundane (How do I comment out statements in ASPX files? ) and the sublime (If I update session state, should I lock it, too? Are concurrent accesses by multiple requests executing on multiple threads a concern with session state?). At any rate, guaranteed to contain a few things you didn't know you needed to know about ASP.NET.