This application allows you to read large Text (.txt,.text), Palm Doc (.pdb), Mobipocket (.pdb,.prc,.mobi), Plucker (.pdb), HTML (.htm,.html), and FB2 files quickly and efficiently on the iPhone. This application lacks many of the advanced features of ruBooks or Books.app, but it can quickly load and display large text files that currently cause Books.app or other UI Text View/Web View based apps problems.

http://code.google.com/p/iphonetextreader/