DjVu, pronounced "deja vu," is an advanced image compression technology that simplifies the difficult process of scanning and digitizing paper documents in a format that captures enough detail to be useful but in files small enough to distribute online. Developed by AT&T Labs in 1996, it's since been advanced by an open-source forum of the same name. It's gaining in popularity since it promises to make available tons of books, magazines, and other important stuff that otherwise would come in files much too large to be hosted by anyone but the likes of NASA.
One of the free DjVu viewers on the scene is WinDjVu 1.0.3, which decodes DjVu files in all versions of Windows from 98 to 7. It's like all utilities should be but rarely are: fast, compact, competent, and a bit elegant, considering how much it packs into a 3.29MB image viewer. It has a tabbed, browser-like interface with a typical Windows toolbar and a scrolling side panel displaying file thumbnails. The top tabs function like browser windows, displaying selections, while side tabs access functions like Search Results and Bookmarks. A minimalist Help file links to considerable online documentation. Some printing options round out the package. You have to see DjVu images to appreciate them, but you'll be seeing more of them soon, so you might as well be ready.
WinDjVu is freeware. It installs and uninstalls easily. But with DjVu files sure to proliferate online, chances are you'll have plenty of use for it.