iOS Fonts
A handy list of installed fonts on the iPhone and iPad.
App Shopper: WhatTheFont (Reference)
Like Shazam, but for fonts. Snap a picture of some text on your iPhone and this app will phone home to the WhatTheFont mothership in order to identify it for you.
Related links
The Typography Manual - For the iPhone and iPod Touch
A glossary of typography that you can carry around with you.