Hey! I'm @rstacruz and this is a modest collection of cheatsheets I've written.
A large collection of freely downloadable cheatsheets and quick reference guides for many things, from .NET to Ada, Debian Linux to EMACS, Sendmail to religion.
The canonical list of OWASP cheatsheets for secure programming best practices.
A collection of quick-reference sheets for two or three dozen programming languages, from PHP and Python to Standard ML, Erlang, and MATLAB.