iOS: Any To Do is a to-do list manager for iPhone that does a great job of helping you sort out personal and professional tasks, and uses the Steven Covey "Four Quadrants" method to help you decide what's urgent, what's important, and what's worth dropping everything to take care of right now.
Covey's Four Quadrant method, first discussed in the book First Things First is an organisational method that asks you to organise your tasks into four categories: tasks that are important and urgent, important but not urgent, urgent but not important, and neither important or urgent. As you add tasks, the app will ask you questions that will place them in each category. When you've finished, you can look at all of your to-dos, just your personal ones, or just your professional ones, either in a more traditional list based on due-dates and dates entered, or in the four quadrants so you can decide what's really worth doing.
Any To Do also syncs with Evernote, so if you already use Evernote to manage your to-dos and projects, you don't have to re-enter everything to get started. The app will also automatically add to-dos with due dates to your calendar so you won't forget them. When you're finished, Any To Do wants you to have a list of your next actions organised by their real priority, not just their due date. The app is $6.49 in the iTunes App Store, and is iOS only.