Microsoft has confirmed that it will be selling Windows 10 on bootable USB flash drives instead of optical media. This will allow consumers to install the OS even on machines that don't have an optical disc drive built-in, such as some of the ultraportable notebooks. The USB drives will also likely be a good bit faster than the discs, making the process quicker.
The OS is now currently up for pre-order on Amazon and is available on a USB drive. You can pre-order the Home edition for $119.99 and the Pro edition for $199.99, if you don't have an existing Windows machine that you can update for free.