so I bought the mb air today (couldn't pass it up for 899 at best buy) and need to erase my old macbook so I can sell it. What's the easiest and best way to do this? I want to sell it with a clean os and I don't have any OS media or usb keys.
Buy or find a 8GB USB drive. Then create your own install media.
Alternatively use Internet Recovery.
Be sure to wipe the drive in Disk Utility before you reinstall.