Future Me - Send an email to your future self
HEY - Email at its best, new from Basecamp.
Dabble Me - Your own private place to write. A journal/diary to help you remember what's happened in your life.
Horde - Horde Groupware is a free, enterprise ready, browser based collaboration suite.
Letter to Yourself - Send a physical letter to your future self
InstAddr - Disposable email address application.