Craft is a meticulously-designed note-taking app for iPhone, iPad, Mac, Windows, and the web. It's well integrated with OmniFocus and is a great place for reference information and project support notes, whether you're using it individually or as part of a team.
Evernote is a natural complement to OmniFocus. Use it to store ideas for upcoming projects and as a repository for project reference material.
A highly-flexible, cloud-based app that individuals and teams can use to write, plan, collaborate, and get organized.
An email client for Mac and Windows that's speedy, customizable, and extensible. The Mac version includes native support for OmniFocus.
Create OmniFocus actions, action groups, and projects more quickly and accurately by defining TextExpander snippets for frequently typed words and phrases.