QuickNFO
Mac OSX QuickLook Plugin for previewing NFO files
Uses libiconv to convert the nfo text to utf8 and then lets WebKit render the output. Seems to work well (at least for the few cases I have tested).
The current version supports preview and thumbnail generation. Rendering with HiDPI, like on retina displays, is also supported.
Installation
Build the xcode project or download the compiled plugin. Then copy the file QuickNFO.qlgenerator
to the path Library/QuickLook
inside your home directory.