The old-fashioned to-do list, which lets the brain concentrate on the task at hand rather than on others in the future, remains one of the world's best productivity tools. These fresh new sites let you keep track of your obligations and prompt you to keep up the pace.
Winner: RememberTheMilk reinvents the to-do list in a snazzy interface that lets you make lists in configurable categories, all laid out on the front page as tabs. Adding to-dos is easy, though adding deadlines, notes, and time estimates is unintuitive.
You can add to-dos using natural language such as "Call Ted next Thursday," sync with your calendar via the widely supported iCalendar format, and set tasks such as "Pay credit card bill" to recur. RememberTheMilk sends reminders through instant message, e-mail, text message, or a combination of these. You can also upload tasks via a special e-mail address that the site gives you.
It's a tremendously well-rounded free product, with neither more nor less than you need to get and stay organized.
Runner-up: Hiveminder is a bit prettier than RememberTheMilk and relies on tags, rather than categories, to group tasks. While you can't set the time and date for tasks using natural language, you do get a nice drop-down calendar, and you can easily edit or add tags to a group of tasks.
Hiveminder syncs with external calendars, publishes RSS feeds, and lets you e-mail tasks, but the only notification it offers is a once-a-day e-mail. In addition, tags are more difficult to track than categories, and while Hiveminder has a more intuitive interface than RememberTheMilk, it doesn't feel as useful in practice.
Also-rans: Those who prefer minimalism will love 37 Signals' Ta-Da List, where you can build multiple to-do lists. It allows no tags, categories, or time elements--just lists of tasks with check boxes. You can make the list public or subscribe to it as an RSS feed, but it won't send you reminders.
Backpack, Ta-Da List's older sibling, lets you create five shared pages that can include to-do lists, notes, and a shared wiki-style document. It will send you up to ten reminders via e-mail or text message, but these are oddly separate from tasks, which, as in Ta-Da List, have no time element.