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.

If you are willing to jailbreak, Action Menu does what you are looking for. I have put my e-mail address in the favorites tab of that program and I can now reach it anywhere.