I was one of the afflicted and lost Stanza after the iOS5 upgrade. I still think Stanza was the best reader for the iPhone by far. I like the way the display is customizable (though it seems so much harder to do than Stanza). I also like the full-screen aspect of this. However, it seems to crash when browsing online catalogs - I havent managed to download anything yet. Stuffing ebooks into it from iTunes works well. Some other ones to look at are probably shubooks and megareader.