If you deal with EPUB (electronic publication documents), you should check out EPUB Viewer for Mac OS X (US$29) from Enolsoft. EPUBL is a a free and open e-book standard by the International Digital Publishing Forum (IDPF). Files have the extension .epub.

Featuring zoom-in, zoom-out, bookmarks, scrolling, printing and more, EPUB Viewer lets you open and read non-DRM protected EPUB eBooks on a Mac, as well as convert EPUB docs to the Adobe PDF format. You can open and view multiple EPUB files in Tab mode. You can play embedded media files, audio and video in EPUB files. EPUB Viewer lets you manage EPUB eBooks on a bookshelf .

You can rotate or Bookmark EPUB files. Converting EPUB docs to the PDF format retains the original elements, including layout, text, images, hyperlinks, tables, fonts, and graphics.