Emacs users, don't forget about EmacsWiki.org, a Wiki packed with useful Emacs goodness. Just a few examples:

• Buffer Cycling with Ctrl-Tab in Emacs
• Iswitch buffers, using C-x b with an even smarter sort of completion that matches what you're typing anywhere in the buffer name ('scr' matches '*scratch*', 'Class' matches 'org.whatever.package.Class'), not just at the beginning.
• Tweaking the compile command
• smart-compile.el, a better 'compile'
• Debugging with Emacs
• Programming Effectively With Emacs
• Other nifty tricks
• Emacs History. I especially enjoyed the external link to the story of how XEmacs came to be, which also links to this explanation of differences from the XEmacs site. I'm currently trying to determine if the relatively new Emacs 21 can win me back from XEmacs, with the features and usability improvements present in XEmacs that caused me to avoid Emacs 19/20 when I was first starting out. I'm very much a novice and probably wouldn't notice most of the differences, but if I'm going to get a little deeper into Emacs, I feel I'll need to pick a camp, or at least understand the differences.