Newegg has listed prices for OEM copies of Windows 7—technically intended for little computer building businesses, but there's nothing stopping you buying them. And as long as you understand some mostly-minor limitations, you can save some serious money.
Take a look at the table—that's not chump change. Newegg is also taking a further $5-$15 off some prices for pre-orders before October 20.
The main two caveats: OEM product keys aren't transferrable from one PC to another, and you'll need to install them on a formatted machine (usually the best way, anyway). Less of a concern is that you don't get any support or packaging; just the disc. Still sounds like a bargain to me—unless you're a college student, in which case you can pick Windows 7 up for just $30 bucks. [Newegg via ComputerWorld via ArsTechnica]
|Windows 7||Home Premium||Professional||Ultimate|
|Full OEM (3 Pack)||$310||N/A||$550|