Evernote
Evernote is a natural complement to OmniFocus. Use it to store ideas for upcoming projects and as a repository for project reference material.
FastScripts
OmniFocus for Mac (Pro) can be automated through the use of AppleScript. FastScripts makes accessing these scripts quick and convenient.
Hazel
Using Hazel for Mac and a little AppleScript, actions can be automatically created in OmniFocus for Mac (Pro) as files are added to specific folders.
Keyboard Maestro
Use Keyboard Maestro to quickly access OmniFocus features and perspectives through global hot keys and to tap into OmniFocus' AppleScript support.
MindNode
Allows you to create visual outlines of your ideas and responsibilities. Useful when designing your system and planning projects.
SaneBox
A web-based service that helps you to tame your email and that reduces the need to create and manage Waiting items in OmniFocus.
TextExpander
Create OmniFocus actions, groups and projects more quickly by defining TextExpander snippets for frequently typed words and phrases.