I've been using the free Tadalist service lately to keep track of my TODO lists. It has a deceivingly simple user interface, but for me at least it turned out to be a powerful ally in keeping on top of my ever-increasing TODO lists.
In Tadalist you can only do a few things: create a list, add an item to a list, edit the list title, edit the description of an item, check off an item as done, and reorder the items in the list. It turns out this is really all you need. I especially like the feeling of checking off an item and seeing it drop to the bottom of the list, in smaller font, joining the list of tasks that are DONE! It's almost as addictive as seeing those dots when you run unit tests. Reordering items is also a very nice feature, because an item that wasn't so hot yesterday can become really critical today, in which case you want it at the top of the list.
One feature I'd like to see is for checked off items to also get a timestamp, so you can go back and see when exactly you completed a given task.
If you're not using any task management software (in which case I hope you're still using old-school pen and paper), then give Tadalist a try.
BTW -- what task management software have YOU used successfully? Please leave a comment.