If you can get past his 1990s era web site, ZuluReader is decent book reading software, and the only one I know of for epub files. It currently has problems reading calibre 6.x files, but the author said he's working on that.
I use ubook for html and other formats (
http://gowerpoint.com/uBook_main.html). It's an extremely powerful reader, with annotations, skinning, etc, but it does not support epub properly yet, and the author's been a little quiet for several months.
Cheers, Carl.