I have no advice on best practices for registration agreements or links to refer you to. I would say it depends on the purpose of the site. I would look at sites with similar purpose. If you're working on a church site for example, I would look at other church sites and find example verbiage. Be aware that these agreements may also be copyrighted and if you copy significant portions it might be best to get permission before using verbiage you find. If you just get ideas and then write your own I think you will be on track.
Hope it helps,