The Consent Section from keepingitkinky.com has some good basic descriptions of consent models and why consent is important.
The consent section from submissiveguide.com has a more in depth description of consent with links to further resources.
Rope bottom Guide. Because rope bottoming is one of those things in kink where clear and accurate communication sometimes is the difference between injury and a great scene.
Erotic Hypnosis Negotiation Checklist by Professor-x. Requires Fetlife login.
Scene, sex, and relationship negotiation worksheets by Pervocracy. The worksheets are free to use, share, and/or modify!