Quick Image Viewer (QIV) for Linux/Solaris/FreeBSD
QIV has been my image viewer of choice for Linux for at least 4 years. It’s very fast and very bare bones, with some on-the-fly read-only image manipulation (brightness, gamma, contrast). Don’t expect thumbnailing, cataloging or any features like that out of it. My favorite feature is attaching scripts to the 0-9 keys which I use to organize images and perform pre-determined manipulations on images (ex: resize to 800x600 w/ ImageMagick). I often wish it had the ability to output the on-the-fly edited images… if I have time and am motivated enough, I might attempt implementing that.