Comic Seer is a free comic reader for Windows and Linux.
The program supports the essential file formats only (CBR, CBZ, ZIP, RAR and images), but whatever you open is displayed in a very capable reader. There's a 4x zoom slider, fit width/ height/ all and full-screen viewing modes, a magnifier (mouse over an area to see a magnified view), rotate left/ right buttons, single or double-page display, and a Browse mode which also displays clickable thumbnails of each page.
If you like to multi-task then Comic Seer can open several comics at the same time, displaying each one in its own tab. These comics are by default saved and reloaded between sessions, but even if you explicitly close a particular file, Comic Seer will remember and restore your last-read page when it's next opened.
A built-in bookmarking system allows you to tag a particular page and quickly restore it later.
A "Comic Information" viewer displays metadata for individual comics, if they have any (ComicInfo XML and ComicRack formats are supported). The program can edit this, too, although only if you install a third-party helper like ComicTagger (the interface offers some help to set this up).
Large comic collections can be sorted into libraries, too. There's not a huge benefit to this, but it does help you group a series together, and a built-in search tool makes it easy to find the comics you need.
An excellent comic viewer with plenty of handy bonus features