If you're looking for a new 360, you'll want to check the label on the side of the box. The power information should read 175w. Older consoles ran at 203w, so 175w assures you a 65nm chip and a Falcon motherboard. Other information to look for on the label is which team manufactured the console, the console's lot number, and manufacture date. Look for the following info:
- Team FDOU
- Manufactured on or after 8/24/07
- Lot number 0734 (on the Halo 3 SKU) or higher (on any SKU)
If you've already picked up an Xbox 360, you can look for the same information on your power supply (the brick), which should also read 175w.
Keep in mind that the methods above aren't the only ways to check to see if your console is a Falcon. There are also other checks you can perform with a flashlight and a sharp eye. You can find them by hitting the "Read" link. Checking the wattage information is still the easiest thing to consider. Right now it's the best way to guarantee yourself a more reliable console, especially if you haven't bought one yet. If you can confirm 175w on a console with a different team, earlier manufacture date, or lower lot number, let us know in the comments.
Update: Clarified some information regarding other methods of checking consoles for Falcon components.
[Thanks, James Taylor]