Apple is ditching all of its traditional MacBook ports for a single USB Type-C connector in its new 12-inch MacBook. It's a smaller reversible connector, and it's not compatible with existing full-size USB accessories. If you want to charge, use a monitor, and use a USB device all at the same time, then you'll need a $79 accessory. There are two options: VGA or HDMI; they're both $79 and sold separately from the base $1,299 price of the new MacBook.
Those who just want to use a USB accessory and not charge at the same time can opt for a $19 USB to USB Type-C adapter. Be prepared to get your wallet out for these new accessories if you want your new MacBook to be useful once you unbox it, though. Sadly, there's no adapter for those who need ethernet connectivity or SD cards, so you'll need to use USB to USB Type-C for both. If you simply want a spare power connector for a new MacBook then you'll need to pay $78, that's $29 for a 2-meter cable and $49 for the actual power block. Yes, they're both sold separately.
Verge Video from CES 2015: This is the reversible USB plug of your future