Any hour now, Microsoft will shut off the tap for downloads of the Windows 7 Release Candidate—a free, almost-complete test version of the OS that you can use for free, uninhibited, until March of next year. Not that most of you will need reminding, but there are plenty of reasons to try it out.
Microsoft will still hand out RC license keys for an undisclosed amount of time, just not the actual OS files, so don't trip over yourself too much. Just make sure that if and when you find your ISO elsewhere—it'll be called something along the lines of Windows 7 RC 7600, the newer the better—that you make sure it's clean. [Windows 7 on Giz]