Windows only: Graphical to-do managers are great, but they often distract you from what's really important. Todotxt.net manages your tasks in a plain text file, so you can spend less time manging your tasks and more time working on them.
Todotxt.net is actually a graphical version of Lifehacker's very own Gina Trapani's Todo.txt, originally a command line application and now an Android app. If you aren't a big fan of the command line, though (or you don't want to use Cygwin on Windows), Todotxt.net can manage your plain text to-do list from a GUI.
Unlike a lot of other graphical text managers, you barely have to do any clicking around, either. Just hit a few keyboard shortcuts, type in your tasks, and get on with your day. You can also filter out certain tasks or projects, or sort them in a myriad of different ways. It does a good job of taking the command line out of the equation without getting rid of what Todo.txt is all about: simplicity and minimalism.
Todotxt.net is a free download for Windows only.