Here are some security features from SQL 2000-2008 that I find relevant to SQL Server Security:
SQL Payment Card Industry Security
http://www.parentenet.com/news/0904_whitepaper.pdf
SQL Server 2008 Security
http://www.microsoft.com/sqlserver/2008/en/us/security.aspx
SQL Server Security Best Practices
http://www.microsoft.com/sqlserver/2008/en/us/Security.aspx
http://www.microsoft.com/sqlserver/2005/en/us/Security.aspx
http://technet.microsoft.com/en-us/library/cc966456.aspx
http://technet.microsoft.com/en-us/cc984178.aspx
http://vyaskn.tripod.com/sql_server_security_best_practices.htm
Security Overview for DBAs
http://www.microsoft.com/sqlserver/2008/en/us/wp-sql-2008-security.aspx
SQL Server Common Criteria & SQL 2008
http://www.microsoft.com/sql/commoncriteria/certifications.mspx
http://www.cisecurity.org/bench_sqlserver.html
http://www.commoncriteriaportal.org/files/epfiles/0520a.pdf
SQL Server Compliance
http://www.microsoft.com/sql/compliance
http://sqlcat.com/msdnmirror/archive/2009/04/15/sql-resources-for-compliance.aspx
SQL Server Security Blog
http://blogs.msdn.com/sqlsecurity/default.aspx
Center for Security Benchmarks for SQL Server
Dept. of Defense & SQL 2008 Security
http://iase.disa.mil/stigs/checklist/db_srr_checklist_sql_server_v8r1-2.pdf
Microsoft vs. Oracle DB Security
http://www.ngssoftware.com/research/papers/comparison.pdf
Implementing Row- and Cell-Level Security in SQL Server 2005
http://technet.microsoft.com/en-us/library/cc966395.aspx
Payment Industry Security Practices
Courseware
2787A Designing Security for Microsoft SQL Server 2005
4614A Designing Security for Microsoft® SQL Server 2005 Designing Security for Microsoft® SQL Server 2005
4615A Designing Security for Microsoft SQL Server 2005
SQL Security NewsGroup
microsoft.public.sqlserver.security