iPhone Application for Email Address Shortcut
An excellent application for shortcuts is Smile Software's TextExpander touch. Because of limitations in iOS, it doesn't work to expand shortcuts in every app (including, sadly, all of Apple's apps). From the manufacturer's site:


  Given the current feature set of the
  iPhone OS, TextExpander touch cannot
  work in the background (as it does in
  Mac OS X), expanding text snippets
  while you work in other apps, except
  for apps with TextExpander-integration
  built-in. You must first compose your
  text in the TextExpander touch Compose
  screen, and then transfer it to
  another app.