MComix is a comic book viewer that can read images from plain image files and from compressed image archives (cbr, cbz, zip, 7z, ...).
MComix is a fork of the Comix project, and aims to add bug fixes and stability improvements after Comix development came to a halt in late 2009.
Open a terminal window and run:
sudo add-apt-repository ppa:blca/ppa -y && sudo apt-get update && sudo apt-get install mcomix -y
Once installed MComix is available under the Graphics section of Xubuntu's Applications Menu.