What's a really good and effective to-do/idea management/brainstorming/scheduling application for OS X?

I own two companies, lot’s of stuff to do every day in business and private life, but it also seems I’m borderline ADD really with a touch of messy.

Problem is, I really kinda do everything right on top of my head, right then and there. Therefore, often stuff/ideas simply get(s) lost again, or high-priority stuff takes the backseat to lesser priority routine tasks.

Is there any application, that really helps to “put it all together” and into action in the right order?

Mind you, my ADD-like “messiness” kinda prevent me from doing anything that remotely resembles an organized approach. So, any MS Outlook/Project -like approach really doesn’t work for me, as I simply don’t have the “discipline” to sit down, enter it all in there and then keep progress updated. It seems hopeless :/