PastPost - Send a letter to your future self
Future Me - Send an email to your future self
Futurospective - An app that let's you record messages to your future self
Dabble Me - Your own private place to write. A journal/diary to help you remember what's happened in your life.
Future Posties - Easily set objectives, targets or goals for yourself by writing an email postcard to your future self.
Letter to my future self - Letter to my future self is a prominent email scheduling service that gives you the opportunity to create a letter with goals and thoughts for your future self and schedule a date for sending it.