Free email reminder site... people enter in specific messages that they would like emailed to themselves "Later" e.g.
ON: December 23, 2002
MESSAGE: Buy birthday present for wife
If you implement a graphical "check" like for instance on MarketLeap, you prevent the system being used by spammers and if you limit the length of messages to 256 characters (e.g.) it can still be useful without being too much of a drain on server resources...