Not sure if anyone's posted or recommended this before, but I've used this a while ago, and just recently remembered it.

yBook is a fairly awesome bit of software. It'll read rtf, html, txt, brn, bfl, prc, pdb, and epub files, and displays it in a book-style layout.

It also lets you bookmark your place, so closing and sudden loss of power is no longer nearly as annoying.

A few other nifty features are that you can specify fonts and font size, search the text for a word/phrase, set a texture if you wanna read on a thousand year old parchment or some other fancy material, or if you don't want fancy background, just customize the colors for yourself. Screenshot Below.



Comes with quite a few built in languages as well...



And best of all; Its completely and utterly free. Not even adds, forced waiting, requests for donations on every open, or pop-ups.

Runs in Windows and in WINE on the Linux flavor of your choice perfectly.