Cinch, an Aero Snap for Mac
Mac OS isn't exactly well known for its window management. Generally, when a user clicks the maximize button on an application window, Mac OS simply maximizes the window in height and doesn't change the width. This isn't what users expect when coming from Windows or GNU/Linux.
Speaking of coming from Windows, a lot of users are accustomed to Aero Snap. Aero Snap is a feature that gives windowed applications a quick way to maximize or take up half of the screen (either horizontally or vertically). This happens when a user takes the app's title bar and knocks it against an edge of his or her desktop. For instance, knocking a window against the right edge will cause the app to take up the right half of the screen real estate. This feature comes in handy quite often.
So wouldn't you like an Aero Snap-like app for Mac OS? Well Cinch is your guy. This app works just like Aero's Snap and is available for free. The free version will ask you to buy the full version from time to time, but that is the only difference that I have seen. Buy it for seven bucks and it won't bother you at all. You can check it out here.