Tim O'Reilly has suggested a code of conduct for bloggers. Seems a bit unnecessary as it just lists things which people should or shouldn't do anyway whether its a blog, website forum, newspaper whatever.
e.g.
We define unacceptable content as anything included or linked to that:
- is being used to abuse, harass, stalk, or threaten others
- is libelous, knowingly false, ad-hominem, or misrepresents another person,
- infringes upon a copyright or trademark
- violates an obligation of confidentiality
- violates the privacy of others

If you can't link to content that is 'knowingly false' what about sites like theonion.com whose whole content is spoof news. (latest headline 'U.S. Asks Africa Not To Cash Aid Checks Until After Tax Day')

Why not just say 'Be good' ?