Is that "Sent from my iPhone" message starting to get on your nerves? By default, every email sent from your iPhone gets appended by a signature specified in Settings > Mail > Signature. To clear out this signature entirely, delete all the text from the Signature text field. Your emails will lose that "Sent from my iPhone" tag.
Of course, if signatures don't particularly bother you, you might want to add a more personalized quote or even some contact information (although preferably not using unnecessary ASCII art). Or, you can put on your antipersonnel hat and start messing with people's minds, e.g. "Sent from my Blueberry." How do you intend to sign your emails?