Evince

Evince is an ebook reader that supports formats like PDF, DJVU, TIFF, Postscript and DVI. Of that list, it seems that DJVU should be the number one addition to the basic XML/HTML support in Sugar. DJVU adds the ability to use scanned book pages without the bloat of PDF. The DJVU compression format is specifically designed for scanned text and achieves better result than general image compression techniques.

More info here http://www.gnome.org/projects/evince/