This is the best ebook reader I've tried (Edit: As pointed out in the comments, Calibre looks much nicer. Give it a shot first). It works for epub, fb2, html, mobi without DRM, and some other less common formats. The menu is a little bit confusing, but otherwise it works very well. Apparently it also works on android.
By the way, if you want to discuss books, head to /f/Books. I just became a mod there, and posted a list of free online libraries.