Rearranging the sections in the sidebar of Finder windows used to be a beast. That hasn’t been the case since the introduction of Mountain Lion.
You can drag and drop sections like Favorites, Devices, and Shared to reorder them however you’d like. And when you do so, the change is immediately effective in all Finder windows already open.
Even better, of course: The change is reflected in any new Finder windows you open, too.

Source: Mac OSX Hints