OEM Versions of Windows 7 Now Available for Preorder

"But you can also pick up an OEM license that's designed for system builders. These OEM copies offer most of the features found in a full retail version, but the license can't be transferred. Once it's installed on a computer and activated, it's locked to that hardware. You won't get any support, and you'll have to perform a clean install, not an upgrade. The upshot is that OEM copies of Windows are typically cheaper."

If you didn't take advantage of some of the preorder opportunities or don't have access through school or work to discounted copies of Windows 7, OEM copies are another option for getting a deal on the OS.  Depending on the version you are looking for, you can save almost half off the price of the non-OEM versions.