There were a lot of Accessories for the Atari 2600 Series. Some from Atari, some were third Party. The importantest
Items are listed here.
Compumate Homecomputer-Keyboard
About the Compumate Homecomputer-Keyboard look the extra page: Atari 2600 Heimcomputer
The Atari Kids Controller with extra-big keys
The Atari Keyboard Controller (Keypad)
The Atari Paddles for games like Breakout
The Atari Indy-Paddles with 360-Degrees for Indy500
Atari Cartridgebox with Eject-Button
The Atari Joypads and Joysticks