IWantSandy is an email-based automated personal assistant that has just opened up for public signups. I've been using Sandy for a couple months now, and she's fast becoming indispensable for my life. All you do is CC your personal Sandy address on your mail and throw in keywords, like "Sandy, remember that this is the grocery list" or "Sandy, remind me to follow up on this with Fred on January 1, 2008" and the Sandybot will file away all your minutae for you. Sandy emails you with reminders (she can also communicate by Twitter/SMS). She can barf up all your remembers whenever you need them -- just tag your emails with the @-mark (for example @phonenumber @kids @kitchenrenovation @welding) and then ask her for all the items corresponding to a given tag.
The coolest thing about I Want Sandy is the "groupware" function -- if I CC you and Sandy on a message with a reminder, she'll remind both of us. No permissions, no groups, just CC in regular email. The service is free and live and open to all comers.
Sandy's a real Boing Boing-pal effort. It was invented by Rael Dornfest, the former CTO of O'Reilly Media, who (among other things) created the open-source blogging tool Blosxom and chaired the O'Reilly P2P and Emerging Tech conferences. Sandy herself is based on Tim O'Reilly's stellar personal assistant, also named Sandy. And bonus -- the little Sandy logo was designed by our own Mark Frauenfelder! The functionality in IWantSandy is really geared to personal-productivity freaks like me, who were inspired by books like Getting Things Done and the Life Hacks movement.
(Disclosure: I am proud to serve on the advisory board for values of n, the company that produces I Want Sandy)
See also: Meet Sandy -- free email assistant