Programming and T-SQL: Henderson, Ken. The Guru's Guide to Transact-SQL. Addison-Wesley, 2000.
Vieira, Robert. Professional SQL Server 2000 Programming. WROX Press, 2003.
SQL Server Books Online: Building SQL Server Applications
Specific Function Reference:
For information about standard deviation and variance, try the Internet Statistics Glossary, located at http://www.animatedsoftware.com/_statglos/statglos.htm.