Instantly switch between Vertex, Edge and Face selection while you are in the edit mode.

"Ctrl+tab 1, 2 and 3. Come on man, it is in the menu if you look." -A guy who reads the manual before he does things.

Link: http://blenderartists.org/forum/showthread.php?213343-Keyboard-Shortcuts-to-switch-to-vertex-edge-face-Select-Mode