DisplayFusion - DisplayFusion will make your multi-monitor life much easier.
SwitchResX - SwitchResX is a tool designed to manage resolutions of all your monitors and HDTVs.
WindowGrid - Quickly and easily layout windows on a dynamic grid using just the mouse.
EasyRes - EasyRes is a fast screen resolution switcher for Mac OS X with live animated previews.
Mizage Divvy - Divvy is an entirely new way of managing your workspace.
Resolutionator - Resolutionator makes it simple to use any of your display's available resolutions.