Did today's Microsoft press conference sell you on the system? If so, then you're probably going to want to pre-order it to make sure you get the console on the very first day. Microsoft used their official news site to reveal that you can get a few exclusive extras if you do so.
The content consists of a limited edition controller. The button layout and design are exactly the same as a regular Xbox One controller minus one thing. On the center of the controller it says "DAY ONE 2013". Players also get an exclusive Achievement, which seems the far sillier selling point.
Pre-ordering directly through Microsoft or other other participating retailers (Amazon, Best Buy, GameStop, Target, Toys 'R Us, Wal-Mart) grants you the exclusives. Xbox One is out this November for $500.