DesktopAid for (X)Emacs, automagic loading and saving of the session when starting and stopping (X)Emacs. It is also possible to save the session at any other moment in time. This will enable you to have multiple session configurations.
the emacs wiki, which collects elisp code, questions and answers related to elisp code and style, introductions to elisp packages and links to their sources, or the source itself, complete manuals or documentation fragments, comments on Emacs and XEmacs features, differences and history, ports, jokes, pointers to clones and emacs-look-alikes, as well as references to other emacs related information on the web.