I can also vouch for OmniOutliner, though I personally don't use it for task management. I use Notational Velocity (http://notational.net/) for taking reference notes, and for task management I email myself action items and tag them using the GTD system. Gmail's amazing tagging and filtering system and its abundance of single-key keyboard shortcuts make it better than any other system I've tried. I don't even miss being able to edit items; I've gotten used to either forwarding or making a new one, and it's a good tradeoff. I'll write an article about it someday.
For nearly everything else I'll default to OmniOutliner, and I usually have at least three or four windows of it open. I've never found any outlining software that comes close. Favorite features: Rarely lacks a keyboard shortcut I want it to have, has audio recording built in (I'd suggest an external mic for it to be useful though), and exports to plain text, HTML, RTF, and Word.
For nearly everything else I'll default to OmniOutliner, and I usually have at least three or four windows of it open. I've never found any outlining software that comes close. Favorite features: Rarely lacks a keyboard shortcut I want it to have, has audio recording built in (I'd suggest an external mic for it to be useful though), and exports to plain text, HTML, RTF, and Word.