iOS 4 for owners of the iPhone product codes 1,2, 2,1, and 3,1 -- in other words, the 3G, 3GS, and yet-unreleased iPhone 4. Owners of more recent iPod touches are also in luck. Interestingly, the build is 8A293 -- the exact same that was released to developers before as a GM seed -- so Apple apparently found no showstoppers pressing enough to necessitate a new build before pushing it to the public at large. It's coming up in iTunes now, so go on -- what are you waiting for?
[Thanks to everyone who sent this in]