The lever in Redstone can be an important power source, if rarely used outside of a control room. A lever has two states: on, and off. It can be placed on the floor, or on any sides of blocks. When it is off, nothing is effected. When turned on by a right or left click from a player, it's image changes and it directly powers the block it is on. It also powerers all blocks adjacent to it, including above and below. The fact that you can power a wire on the other side of a solid wall with one makes it good for control panels, esp. where you need to keep an on or off state (unlike a button). Using a button and a T-Flip Flop, you can simulate a lever.