The best source for SQL Server internals and advanced TSQL are the Microsot SQL Server development teams' blogs. Some are more active than others, but they're all worth subscribing to for that gem you don't want to miss. For example, the SCHEMABINDING tip is a real nugget.

• SQL Programmability & API Development Team Blog
• SQL Server Engine Tips
• SQL Server Storage Engine
• Tips, Tricks, and Advice from the SQL Server Query Processing Team
• SQL Server 2005: CLR Integration