The keyboard key I like most. It's many uses include:
  1. Indenting paragraphs
  2. Lining up text
  3. otherwise moving the cursor left in a controlled, orderly fashion
  4. Moving to the next field on a form
  5. Switching weapons in Unreal Tournament (provided you have configured your keys in a superior fashion)
It also plays a significan role, along with Alt, in switching programs in Microsoft Windows.

Tab rocks my world. Don't event get me started on Ctrl Tab.