For public domain stuff there's
wikisource, and the html versions of texts at
gutenberg. But it's hard to keep track of where you left off since the text is presented in big chunks, often the whole book on one page.
There's also
Wowio, which I have bookmarked but never used. I understand they offer mostly comic books.
That's all I have, but then I don't like reading online. I'm sure others will have better links
