While I am on the subject of iPhone web apps, Britannica MiE <http://i.eb.com/> is probably my favorite one of all. Although Wikipedia is ubiquitous, Britannica is authoritative. Plus, it never hurts to look up more than one source on a topic. So why a web app and not an iPhone app? Because for something like a large reference that is perpetually updated, a web app doesn't take up space on your iPhone, and the content is always recent.
With Merriam-Webster's dictionary and thesaurus <http://i.word.com/>, and Britannica's encyclopedia web apps, I have the whole reference shelf right on my iPhone.
