Phototonic is a fast and functional image viewer and organizer, inspired by the traditional image viewer design (i.e. thumbnails and viewer layouts)
nomacs is a free, open source image viewer, which supports multiple platforms. You can use it for viewing all common image formats including RAW and psd images.
Geeqie is a lightweight Gtk+ based image viewer for Unix like operating systems.
The Ristretto Image Viewer is an application that can be used to view, and scroll through images. It can be used to run a slideshow of images, open images with other applications