Emailfuture is a web based application that can let you send emails to anyone on a future date and time. The look and feel of this small website is very attractive (atleast I felt so).
You can mail yourself reminders about a future event, anniversary, your girlfriend's or boyfriend's birthday. Send yourself a mail at the end of the day with a reminder to buy grocery or beer cans. There is a long list of activities provided on the website itself, that you can do with the help of this application.
Check out this beautiful site yourself.