I've written a web-based service that allows you to send yourself an email based on a schedule: mailremind.
Why? Because I often send myself an email to remind me of something and I thought it would be useful if I could send mails in the future or based on a schedule (e.g. useful for birthdays).
If you also think this is useful, you can have your own installation (it is quite easy to configure), or you can use my public mailremind installation: mailremind.silvasur.net