Jumsoft Process is a very nice outliner for OS X. It can handle projects as separate files but from the same interface, which is nice and enables easy tracking of workflow. You can easily manage due dates and priorities and link files relevant to your tasks. In my brief test the only real issue I have is that there is no direct link to iCal for Datebook and ToDo management and notification via Treo. I’d love to see that added as it would make like much simpler than having to rely purely on the computer… You can export to iPod among other locations and file types, which is helpful – just not to my usual workflow.
It’s only $25 and there’s a 7 day unlimited trial period.