Canon ZoomBrowser

If you have a Canon camera, it's worth getting the newest version of ZoomBrowser EX (5.8b); the 5.8 series adds a very good "zoom" view which is a bit like the Windows Explorer thumbnail view except that you can scale the thumbnails up as big as you want. This makes it really easy to pick between duplicate shots taken at different exposures, etc. ZoomBrowser is a nice piece of software, for being free (for Canon users).