Remembering all of the available Group Policy settings can be a headache. Here’s a handy link to downloadable spreadsheets containing a complete list of Group Policy Settings for all recent version of Windows and Windows Server (as well as details of which .adm/.admx file the setting is part of and which registry key is changed by each setting!):
Group Policy Settings Reference for Windows and Windows Server
If you’re only interested in learning what’s new in Windows 8/8.1, a reference is provided here: