If you don't see an add-on provider that was on the old site you can go to them directly via their url. For instance Loggly isn't there but you can go to...
Updating documentation to be consistent with the rest of our add-on docs in Dev Center is a requirement for being displayed on the main page. We're still working with a few providers to bring them in line.
https://addons.heroku.com/addons/loggly