If you find one, I'd be very happy to hear what it is! I've been enjoying reading books in the Kindle app on my iPad and my Android phone, but that only works for books I buy from them. (I was able to load a non-Amazon ebook into the Kindle app on the iPad, but of course it doesn't sync bookmarks or anything since it's not theirs.)

My wishlist has one additional item: the ability to reset the "furthest read" marker, so that when I re-read books I can still move easily from device to device without losing my place. All the apps I've used so far assume you go through a book once and then you're done. (Weird assumption!)