DisplayFusion - DisplayFusion will make your multi-monitor life much easier.
Magnet Window Manager - Magnet Developers
Mizage Divvy - Divvy is an entirely new way of managing your workspace.
Spectacle App - Move and resize windows with ease.
WindowGrid - Quickly and easily layout windows on a dynamic grid using just the mouse.
Moom - Move your mouse over the green zoom button in any window, and Moom's mouse control overlay will appear (as seen in the above animation).