Great Apple (first and third-party) accessories or peripherals List your favorite accessory (or peripheral) for your Apple hardware.

Rules


Limit to one accessory per answer.
Add a short description for the accessory.
Add a link to the website in the name of the accessory if possible .
Use ## accessoryName (price) for citing the accessory name.
Check for dupes.


Only Mac OS X and iOS compatible accessories.

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Smart Cover
Apple's Smart Cover for iPad 2 ($39 for Polyurethane, $69 for leather)


The Smart Cover and iPad 2 were made for each other. Literally. Built-in magnets draw the Smart Cover to iPad for a perfect fit that not only protects, but also wakes up, stands up, and brightens up your iPad. That’s not just smart. It’s genius.