iPodDisk - Requires MacOS 10.4 or newer Transfer your music from your iPod back to your computer. Overcomes the need to keep duplicates of MP3 files on your computer, since with this your iPod will work like a hard disk is supposed to work and you can get your MP3 files back unto your computer's hard disk when needed.
Senuti - Requires MacOS 10.3 or newer Transfer your music from your iPod back to your computer.
Overcoming the iPod Shuffle Problem The trouble with the iPod Shuffle is that it can only load MP3 files from one computer. Learn how to solve this problem.
Jacket - iTunes Visual Plugin My favorite visual plugin. Displays info about the currently-playing MP3 file as well as any image that you assign to the file (or album, or artist). You can delete all images within MP3 files, if you want, so you can fit more MP3 files on your iPod, but still have images displaying when playing MP3 files on your computer.
Clutter Displays album art work on your screen of what's playing in iTunes. (An alternative to "Jacket.") This one will automatically download the images and save them to your hard disk, if you don't already have the image. (Jacket doesn't "save.")