I'd have to throw most of the standard UNIX utils in there: grep, awk, cut, sed, sort, uniq, and of course, vim.
Outside of the tech world, people seem to think that grabbing some columns out of a file and rearranging them or pasting them somewhere else is some kind of sorcery.
One unix based utility that has saved me incredible amounts of time is 'vimv'.[1]
You run vimv and you get your pwd, in the editor, and you can edit it like a text file. Then just quit and save and all of your filename changes get committed to that directory.
It's an extremely fast way to do a bunch of random and irregular edits to a big directory full of files.