Of course Project Gutenberg has scores of HTML Public Domain books that will display on any browser:
http://www.gutenberg.org/wiki/Main_Page
If you're willing to use Firefox as a browser there is a nifty add-on that works superbly for .epub files.
Firefox:
http://www.mozilla.com/en-US/firefox/personal.html
The add-on:
https://addons.mozilla.org/en-US/firefox/addon/45281