Here's a nifty idea to add a little organization to your Finder sidebar. Since it does not natively support separators, one fellow decided to hack up a solution
by creating some fake applications whose icons are transparent and whose names consist of line characters. You can then drag and drop these on the sidebar to give the desired effect.
It's a small thing, but a nice one for keeping your Finder sidebar visually tidy. The package also contains a nifty little AppleScript application that will launch the Terminal at the location of a folder dropped on it.