I have just downloaded probably one of the most useful iphone applications. WhatTheFont basically identifies the fonts in a photo or web graphic!

How it works:
You simply take a photo or find a photo in your iPhoto library, it connects to the MyFont servers and will identify the font from your photo!
Amazing for any graphic designer who's out and about and wants to know what a font is they've seen on a poster design or sign.
If you're a designer with an iPhone, this is a must-have! Download it here