Databases:
MySQL Cheat Sheet
MySQL Reference List
SQL Server Cheat Sheet
SQL Server 2005 Commands
Programming:
ASP/VBScript Cheat Sheet
C# Language Reference
C# Programmer’s Reference Sheet
.NET Cheat Sheets
PHP Cheat Sheet
PHP Developer Cheat Sheet
Ruby Cheat Sheet (PDF)
VB.NET Cheat Sheet (PDF)
Web Dev:
CSS Cheat Sheet
CSS Shorthand Guide
CSS Reference Sheet
Javascript Cheat Sheet
Javascript Quick Reference
AJAX Cheat Sheet (PDF)
JQuery Cheat Sheet (PDF)
JQuery Reference (PDF)
Misc:
Ascii Codes Cheat Sheet
Regular Expressions Cheat Sheet
UML Cheat Sheet
Google Cheat Sheet (here and here)