I've been a Windows user most of my life but decided to jump over to Mac. With that jump also came a feature which I sorely missed from Windows 7. That was window snapping. Window snapping was bloody awesome on Windows 7, the whole OS as a whole was bloody awesome, it had little features here and there which were just brilliant. I needed this back and luckily there was an app to just do that - BetterTouchTool.
BetterTouchTool doesn't just do window snapping though. It's main feature is custom gestures. You're able to create nearly any custom gesture you like to accomplish simple tasks. It's ridiculously useful and is a must have. It even lets you assign your custom gestures to specific apps so they don't collide when you move to another app.
Oh and another thing, it's completely free.