Remember The Milk: "Never forget the milk (or anything else) again.
Remember The Milk is the easiest and best way to manage your to-do lists online."
Found through this blog entry.
It provides the following, according to their website:
* Features galore: Sharing, publishing, notes... we've got it all.
* Get reminded: Receive reminders via email, instant messenger, and SMS.
* It's free: Hard to believe, we know, but it's true.