Yes, the Fictionwise ebooks are readable without any modification. Books on Fictionwise can be published as either "multiformat" or "secure". Multiformat ebooks don't have any DRM - except for the users' agreement not to copy. Secure ebooks are available in a variety of formats, none of which are currently directly useful to us.
While most newly-published books are in the 'secure' format, Fictionwise carries a lot of reprinted stories, and older books, in the multiformat format, and you can choose to search just the multiformat ones so you're not tempted by an ebook you can't yet load
I particularly like that you can subscribe to ebook versions of the major US science fiction magazines - and download them as good-looking PDFs for the iLiad.
You can find out more here:
http://www.fictionwise.com