One of the most frustrating things switching from Windows to Mac is window management. Traditionally in OS X windows can only be resized by dragging the lower right corner. With the release of Lion, OS X gained the ability to resize from any window edge. But this still pales in comparison to Windows 7.
Windows 7 provides Aero Snap which allows users to quickly resize windows. Drag the window to the right side of the screen and Snap automatically resizes the window to take up the right half of the screen. Similarly for the left side, drag left and cover the left half of the screen. Snap will also resize a window to the full screen height.
Searching for similar functionality, I found Moom, developed by Many Tricks. Once installed, hover over the zoom button and an overlay appears with some options for arranging displays. At the top there is a list of shortcuts; full screen, left, right, top, and bottom. These are handy when moving files or writing a document. Below the shortcuts is a grid. Click and drag a group of boxes in the grid to resize the window. These few features just scratch the surface of the power of Moom.