A few of my own favourites:
- :windo :bufdo :tabdo and :argdo. Absolutely magic if you've a large number of files to work with. (:help :windo)
- "gq" for reformatting (:help gq)
- Digraphs for common characters not on your keyboard (:help digraphs). Press ctrl-K followed by the two characters to type them in, e.g. ctrl-k, p, * prints a Greek pi(:help i_CTRL-K). Use :digraphs to list them all.
- For other characters, "ga" for finding out the ascii/unicode value of the character under the cursor (:help ga), and it's converse: ctrl-v, u, to type them in. (:help utf-8-typing)
Yes, I do work with a large number of odd characters in my work :). But when you get used to typing them, you start using them everywhere. Just because you can.