XImaging is a lightweight, multi-threaded image browser and viewer for Unix - X/Motif, with basic file management functionality.
Documentation and more on the project homepage: http://fastestcode.org/ximaging.html
SlideViewer is an automatic picture viewer. Just point SlideViewer at directories containing images, and it displays the images as a slide-show.
Convenient controls enable altering the speed, pausing, going-back, and sequencing manually.