A Mac app called Alfred has saved me countless hours. It comes with a clipboard manager (extremely useful), and the ability to create custom workflows/hotkeys, which I use to switch back and forth between Skype, Chrome, and Sublime. iTerm2 already has a hotkey feature built in, but if it didn't I'd have made one (takes <30 seconds).

Following Gary Bernhardt's advice, mapping Caps Lock to a modifier key (he recommends Control I think, I mapped it to Alt) has been awesome.

Aliasing common Git commands to 2-3 letter commands has been nice. gc -> git commit, gaa -> git add --all, gpom -> git push origin master, etc.

Vimium for Chrome is nice if you're used to Vim keybindings for navigating.

hop is a command-line tool for jumping to directories (or SSH'ing into servers). Immensely valuable.