We've been looking to provide a higher-quality, spam-free experience at the plugins site for some time, and a major error on our part forced us to shut down the current site before we could put the new one in place. We are developing a new site, and you can follow along with its development on GitHub. For more information about this transition, including steps you can take as a plugin author to prepare, please read our post about what's going on.
If you'd like the browse the old archive, it is available at archive.plugins.jquery.com.