DuMP3 is a duplicate and similar file finder. It finds exact duplicate binaries by hash, similar text files by substring content, images (JPG, BMP, GIF, PNG, etc) by color and audio files (MP3, WAV, OGG, etc) by wave data. Future: fonts, video.
ImageSorter is image browser/file manager for unix systems writen in perl/glade/gtk and uses imlib graphic library.
It has many advanced features like multiple panes, viewing multiple images, regexp selections, drag-n-drop, finding duplicate files,...