I use BetterTouchTool for this, it lets you set up snapping so dragging the window e.g. to one side will snap it to half the width, as well as setting up keyboa

I use BetterTouchTool for this, it lets you set up snapping so dragging the window e.g. to one side will snap it to half the width, as well as setting up keyboard shortcuts. It can also do a million other shortcut type things which I barely scratch the surface of, cool app!