If you're willing to sideload, Kobo will allow imported epubs and there may be others I don't know of. Free, native apps - none I've found. Of course the sideloaded Kindle is great too.
BookReader, $.99, developer active in these forums.
+1000, but if you really want it to be free, sideloading Android apps is the only decent solution, try Moon Reader, Kindle or Go Book, IMO Book Reader is the best and $.99 isn't that much.