XNView for graphic browsing
XNView is a very good utility for browsing your graphic files. You can get it for free directly here: http://www.apple.com/downloads/macosx/imaging_3d/xnviewmp.html.
XNView can supplement Gimp in the sense that you can manipulate your images using Gimp, but putting all in order through XNView. Sorting, filtering and resizing will remind some of you of the old days with the Norton Commander interface. A very nifty program when you only use a few features, yet powerful enough for you to find new features on a regular basis.
My first tool I will recommend you get is certainly XNView. If you need the program for either Linux or Windows, you should get it from this location: http://www.xnview.com/.