Web/iOS: Eisenhower is a simple and elegant way to sort your tasks. Based on the Eisenhower matrix by former US President Eisenhower, the webapp and mobile app help you identify which tasks to do now, schedule for later, delegate, or not at all.
If you're familiar with time management systems, you've probably seen this matrix before. Essentially, you add tasks into quadrants based on whether they're important/unimportant and urgent/not urgent. Something that's both urgent and important should be added to the top left box to be done right away. On the flip side, tasks that are neither important nor urgent go on the bottom right box as a reminder of what you shouldn't do. (Do-not-do lists can boost your productivity.)
The Eisenhower app takes this approach to helping you evaluate and prioritize your tasks. The app is dead simple to use. Just add your to-dos in any of the quadrants, considering whether each task is important or urgent. You can quickly add tasks and drag them around to reorder them.
I have two wishes for the webapp: That scheduling box actually had a date selector and reminders, and you could check off tasks as done rather than just delete them.
Still, if you're looking for a new task manager or if you're a fan of this system, give Eisenhower a whirl. The iOS app is available for $1.99 (and does have scheduling, a "focus mode," and syncing to the web client), but the webapp is free.