Button

A Button is a block that has the same texture as a block of Stone. A button can be mined easily with the player's hands. It can be crafted by placing two Stone blocks in a vertical row. Like Levers and Pressure Plates, it sends a charge to an object when pressed. However, a button can only be activated by being pressed and will only stay pressed for 0.9 seconds. After this, the charge to the object will be lost and the button will pop out, ready to be clicked again. However, with the creation of a T Flip-flop redstone circuit, it can be used as a lever substitute. Unlike levers and torches, a button can only be placed on the side of a block.

Like any object that gives charges, it must be next to the object receiving the charge (Doors, Rails, etc.) or connected to it by a length of redstone wire.

The button is one of four switches currently in the game. As a momentary-contact switch, it can be useful for resetting redstone circuits.

When submerged in water, Buttons are destroyed, rather than merely becoming unattached, like torches.

Also like torches, buttons can be placed to a side of a chest, dispenser, workbench, or furnace in the same fashion. This is done by placing a solid block above the area the button will attach to, and right clicking it on the bottom with a button in hand. The button can't attach to the bottom of blocks, and will relocate to an available space. This lets you place the button on a block's side without right clicking it.

Natural occurrence
Buttons can be found naturally in Strongholds right next to iron doors.

History
The Button was introduced in the Seecret Friday Update 3. The Button appears in Alpha, Beta and the game's Full Release.

Since Beta 1.5_01, it appears that the hitbox for the button is off. You need to click a space in front of the button for it to be depressed. This was fixed in 1.6.6, with the side effect that you cannot punch through doors anymore.

Trivia
On servers, lag can cause buttons to be pressed for too long.

Edit. this is false at least since minecraft 1.0.0

Steinschalter Bouton en pierre Stone Button/ko Przycisk Кнопка Button/ch