iOS: If you have a problem keeping up to-do lists with due dates weeks from now, free app Do it (Tomorrow) keeps you focused by letting you make tasks for (and move them between) two days: today and tomorrow.
The main idea of Do it (Tomorrow) is focusing on the tasks you need to do right now, and pushing them to tomorrow when you can't. It doesn't clutter up your list with the worries of later in the week, nor does it distract you with labels, tags or different to-do lists — it's essentially two pieces of paper that you can move tasks between with a tap of your finger. It attempts to simplify the to-do list process by only showing you what's looming over your head today, and it does a pretty good job at that. Of course, if you prefer, the general philosophy can be applied to any to-do list app out there — but none of them will handle it quite as smoothly as Do it (Tomorrow) does.
Do it (Tomorrow) is a free app for iOS, though an iPad-optimised HD version is also available for $2.49.