The absolute screaming latest version of Firefox has been quietly published to Mozilla's public FTP servers. Already have binaries for all three primary platforms (Windows, Mac, Linux), Firefox 2 Alpha can be downloaded at your discretion if you like to try out new stuff. With the impending release of IE7 and the hype surrounding it, you'd think Mozilla would put a lot of public attention onto FF2, but it has been fairly quiet so far.
If you're interested in getting a sneak peek at some of the new features, like it's built-in anti-phishing, download and try. Keep in mind it is fully in Alpha stage for development, meaning it has no official support, is only being developed in-house and likely any extensions you currently use with FF 1.5 will not function. But hey, it's new.