Mazarin is an open-source interface to Project Gutenberg's library.
You can access any of Gutenberg's 10,000+ books and have it formated as an e-book in HTML format. Mazarin provides paginations in addition to generating table of contents and other advanced markup features. Of course, you can also view the full book as a single HTML page - wonderful if you are planning to convert it to iSilo or Plucker format.
Pluckerbooks is another good resource which offers Gutenberg text files as HTML or Plucker PDB.