Paddle shifters are the small thumb-operated buttons located just above the buttons for the horn on cars with "manumatic" (and often CV) transmissions.
They tend to be implemented in one of two ways: push/pull for gear down/gear up or left/right for down/up or up/down.
Not as much fun as a standard manual tranny, but it allows you to entertain certain F1 fantasies.
-CW