I want to create a compendium of cheat sheet sites that I think are good for SQL Server. And if I can't find anything good, I was going to create my own.

SQL Server DBA focused

A simplified BOL site includes more than DBA info - http://www.ss64.com/sql

Pinal Dave has attempted to create a one page version for SQL 2008.

SQL Server Developer focused

Development

A very good one with execution plan icons and color coding on what to avoid - http://www.dotnet4all.com/snippets/2008/04/factsheet-for-sql-server-developers.html

Analysis Services - http://www.ssas-info.com/ssas-cheat-sheets

Security Related

SQL injection (contains Oracle, MySQL, PostgreSQL, and SQL Server - http://ferruh.mavituna.com/sql-injection-cheatsheet-oku/

SQL injection quick reference and site also has excellent cross site scripting (XSS) page - http://ha.ckers.org/sqlinjection

SQL injection wiki site - http://www.sqlinjectionwiki.com

NON-SQL Server Related

Regular Expressions ToolBox - Big list of hints and tools for RegEx expressions.