Bill has some useful tips on how to get back to where you were with exchange-point-and-mark (C-x C-x) and pop-global-mark (C-x C-SPC).
Nicolas Lara wrote about converting fontlocked emacs buffers to html using htmlize. As htmlize uses css classes rather than inline styles it uses a snippet from Ruslan’s blog. htmlize-region-for-paste can also convert the css classes to inline styles although it isn’t an interactive function. Doesn’t everyone write their blog posts using muse (with htmlize) which already does this and more?
Amongst other great posts (!), I should also point out my own posts on solving mathematical problems using calc mode and on mapping aliases to dired directories.
emacs-fu wrote a post on querying emacs itself to find out how it does stuff. Steve Yegge mentioned the help functions in his effective emacs post – Item 8: Learn the most important help functions.
Ryan McGuire wrote about using autocomplete.el with python. dabbrev-expand (M-/) is built into emacs and provides dumb but very useful autocompletion. However, autocomplete.el looks a lot prettier.
Joseph Miklojcik wrote a macro to define functions which switch to certain buffers and back again.
