Simple addon that makes the Blizzard windows movable. To move a window just click title of the window and drag it to where you want it. You can also use control+scroll wheel over the title of a window to adjust the scale. The positions and scale will be saved only for the full screen windows such as the achievement window.
DragEmAll is a simple and lightweight addon that allows you to move most default frames, such as the inbox, character window or the achievements window, anywhere you want. The frame positions are not saved.