Cinch

Irradiated Software: There is a feature in Windows 7 that dramatically improves window management, but is absent in OS X. Drag the window to the left of your screen and it automatically resizes the window to take exactly have of your screen. Same thing happens when you drag a window to the right edge of your screen. This is a must-have for me since I tend to open up two windows side-by-side when blogging. But resizing windows on a Mac is a pain, to say it mildly. Cinch is a simple, elegant and must-have utility for dramatically improved window management on the Mac. Perfect.

Update: I have moved on from Cinch to a much more affordable solution called DoublePane.