General SQL Server info

• SQL Server Central - a large site with more than 800,000 members and over 10,000 articles.
• SQL Serverpedia - a wiki/knowledge base edited by Kevin Kline.

Tools

• SQL Server PowerShell Extensions (SQLPSX) (HT: Mark Goldberg)
  The primary goal of SQL Server PowerShell Extensions (SQLPSX) is to provide intuitive functions around the SMO objects which are backward compatible with SQL 2000. A secondary goal is to provide an application which reports flatten/effective security settings.

Blogs

• SQLBlog.com - Around 30 SQL Server-specific blogs 
• In Recovery - Paul S. Randal on SQL Server. Lots of great stuff here.