Another one is Site2GO
There is a free test one. As far as I remember it has a size limit and the special fullscreen option does not work.
There is a very nice menu at top on it but to go real fullscreen you shake the iPad. It works fine on my iPad 3 but not on my iPad1.
The HTML Books is my favorite and it will soon be updated with some of the options I asked him for.
Not sure what he will include but I asked for progress bar for the download, fullscreen option, nicer neutral toolbar, and option to make frontpage on the books by using a default.png just as in the Apple iBooks author.
Hans