The following cheat sheets, covering Apex code, Visualforce, the Force.com Web Services API and formulas, are concise reference guides to each of these technologies - summarizing the most important aspects of each technology in a compact, searchable and printable form. The resources listed below provide access to the most recent version of the online cheat sheet, as well as to the most important reference material.
http://wiki.developerforce.com/index.php/Cheat_Sheets