This post is relevant to iPhone and iPad users who would like to read books on their devices
Yesterday I installed Stanza from Lexcycle (http://www.lexcycle.com/) a very lightwight and robust e-book reader for the iPhone. It supports formats like pdf/html/epub, epub being the most popular
When combined with Calibre (http://calibre-ebook.com/) this becomes your hub for e-book exchange with your PC. You can always download the epub format books from various sources and get them loaded to your iPhone/iPad in like 5 minutes OR you can buy them from countless sources on the net
The interface and bookmarking feature is very clean and Stanza loads books with sizes more than 10MB without any issues.
App has a night feature too, bookmarks multiple books at a time,has font increase/decrease feature plus rotation lock. Pretty much you would want in an e-book reader for your iPhone
In contrast, I also tried some other apps like Bookshelf (which crashed when loaded books with size more than 1.5 MB) and Kobo (not free at all)
For book overs, try this out