Future Me - Send an email to your future self
Roundcube - Web-based IMAP email client
Dabble Me - Your own private place to write. A journal/diary to help you remember what's happened in your life.
HEY - Email at its best, new from Basecamp.
Letter to Yourself - Send a physical letter to your future self
Mailo - Mailo is an email client where you can send and receive emails to and from anyone with an email address.