I don't know when to-do lists suddenly became the wave of the future, but it seems like there's a new to-do list app showing up every other week. This week's is Remember the Milk, a particularly featureful list-keeper. With Remember the Milk you can set due dates for your tasks, assign color-coded priorities, categorize your tasks (e.g. Work, Personal, etc.), create tasks that repeat every day, week, etc., store unlimited notes for each task, get reminders via e-mail, IM, or SMS, send tasks to others people, and undo most actions. The interface is simple and attractive but how to do everything isn't entirely straightforward from the get-go, so some exploring is necessary, but otherwise Remember the Milk is very impressive, and it's completely free to boot.