Magnet - Must have for window resizing if you're used to Windows.
Semulov - Easily eject external drives from the menu bar. Lifesaver with a docked MBP.
Amphetamine - a better take on keeping your Mac awake than Caffeine (an old classic).
There are also Terminal commands that allow you to speed up the cursor speed of your trackpad/mouse beyond what System Preferences will allow. Made a huge difference for me. The fastest speed you can set is 3.0 through System Preferences; I have mine set to 12.0.