Keyboard shortcuts rock. Sometimes you must contort your hands..and this is one of them. Here is how to hide the sidebar in a Finder window. Make sure you have an open Finder window with the sidebar displayed. Now, hold down 'Control-Option-Command-T' To bring it back, repeat the previous command. Alternately, you can click on the dimple and drag it to the right. Also, listener 'Daniel' wrote in to add that you can also double click the dimple to hide/show the sidebar.