SizeUp is SO money - it saves so much time, I'm surprised that Apple hasn't standardized this feature!

Before I started primarily using a mac, I swore by xmonad. SizeUp provides a framework for using shortcuts to tile instead of automatically tiling. After using SizeUp for a bit, I realized I liked its model of things better.

SizeUp allows you to quickly resize and position your windows with keyboard shortcuts or a handy menu bar icon.

This the first thing I install on a new Mac.