DigiKam is an advanced digital photo management application for KDE, which makes importing and organizing digital photos a "snap". The photos are organized in albums which can be sorted chronologically, by folder layout or by custom collections. Supports many plugins and filters and is compatible with most models of digital cameras for transfering pictures with ease.
gThumb is an advanced image viewer and browser. It has many useful features, such as file system browsing, slide show, image catalogs, web album creation, camera import, image CD burning, batch file operations and quick image editing features like transformation and color manipulation.
F-Spot is meant to be an easy-to-use photo management application. It allows for importing of your existing photo collections, tagging photos with identifiers, as well as doing simple edits of photos (e.g. rotating). Newest versions include integration with Flickr photo sharing website.
Gwenview is an image viewer for the K Desktop Environment. It features a folder tree window and a file list window to provide easy navigation of your file hierarchy. Gwenview uses docked windows, so you can alter its layout any way you wish.