An overview of what you can find on origami on this site:
The OSN publishes a magazine, the Orison, full of models in various categories and difficulties. You can find more information on the pagina about the Orison.
Are you looking for diagrams? Check the special page. New diagrams are added regularly.
Reference booklets are little booklets with reminders on how to fold a certain base diagram. The page is currently in Dutch only, but there are English versions of the booklets available.
The links page provides links to all kinds of website containing articles on origami.
[More to come]