– M-x column-number-mode makes Emacs show column numbers.
– emms-locate is a useful way to play selected media files.
– Powerful buffer switching: With either iswitchb or ido, C-x b C-s. ido seems to be better than iswitchb for multitty Emacs, and comes with CVS GNU Emacs. iswitchb is in GNU Emacs and the edit-utils package for XEmacs. If you want to stick with iswitchb fulltime, add (iswitchb-default-keybindings) to your init.el.
- ess (emacs spreadsheet): set-variable set-goal-column nil for neater navigation
- emms: (define-key dired-mode-map [.] 'emms-play-dired) after dired is already loaded
- Editing XML: Many people recommend nxml (GNU Emacs only). xsl-mode is also useful even for other XML files. xsl-mode indentation is better than xml-mode, too. xsl-mode is in the xslide package, and in the cygwin sumo package.
- If you want Python files recognized, install python-mode and (add-to-list 'auto-mode-alist (cons "\\.py\\'" 'python-mode))
- Gnus: You can use B DEL to delete drafts.
- Recursion in lambdas! (funcall #1=(lambda (n) (if (= n 0) 1 (* n (funcall #1# (1- n))))) 5) - result: 120. Not recommended.
- Use M-x goto-line to go to the nth line.
- To copy the font setting and color-theme of the old frame when you create a new frame: (defadvice make-frame (around frob-frame-parameters activate) (let ((default-frame-alist (frame-parameters))) ad-do-it))
- How to get rid of all the ^Ms at the end of lines: M-% C-q C-m RET C-q RET RET . (Better solution: M-x revert-buffer-with-coding-system, dos.)
- desktop can make Emacs jump to the previous position in a file when you reopen the file
- Setting auto-fill in file comments: -*- mode: major; mode: auto-fill -*-, where major is the major mode you want

– ess toolbar variables (customization) need to be set before ess is loaded, but ess is loaded in site-start. How do you set it, then?

– ljupdate darcs repository: http://edward.oconnor.cx/code/ljupdate/
– ERC seems to be the most popular IRC client.
– Have you checked out the Emacs LiveJournal community? http://www.livejournal.com/community/emacs/
– Don’t worry about losing local changes when you modify the source code of CVS Emacs. CVS does patches.
– Emacs under screen: C-\ might be a good Screen escape key.
– People use normal synchronization tools like rsync, unison, and CVS to sync their planner.el pages between computers.
– Hook variables named -hook tend to not take arguments, while hook variables named -functions might be called with arguments.
– Debian: /etc/emacs/site-start.d and /usr/share/emacs/site-lisp/debian-startup.el are responsible for lines like “Loading 00debian-vars (source)…”, while /usr/lib/emacsen-common/emacs-package-install is called when the deb is being set up.