Android 2.2 Froyo starts rolling out for Nexus One
Users on some of the main Android forums have discovered that Google is already hosting a download of Froyo for the Nexus one. Although it takes some doing, you can get it on your phone a little bit early by following these instructions from a developer forum. Because I don't have a test Nexus One on hand, I can't confirm that this installation process works, but the link to the OS download is for real.
Of course, you could always wait a few days and get the OTA update as it (slowly) rolls out.