Aurora - A Mac OS X only application for making it so you can wake-up to your favorite playlist via your computer.
Bandwagon - An automated backup service of your entire iTunes library to a remote server of your choosing. Currently Mac only.
GimmeSomeTune - Built for Mac OS X, gives you a mini-controller with numerous hot keys, downloads album covers, support for iChat and much more.
Goombah - Monitors your play history, compares it to other users and makes suggestions of tracks you may like, and suggests free downloads from their library. For Mac and Windows.
idleTunes - Aids in managing your iTunes library, cleaning out dead tracks, making a playlist for each album, exporting playlists, and more. For Windows only.
iRCTunes - Control your iTunes by integrating controls into the chat programs X-Chat Aqua, mIRC, Adium, X-Chat Windows, Colloquy, and IRCTunes Forum. Works with Mac and Windows.
iTunes Accessory - A Windows Vista enabled iTunes remote control that gives you volume control, album art download, fade between songs and more more.
iTunes Gadget - A remote control for your iTunes, runs in your Windows Vista sidebar.
iTunes Hotkey - Gives you full control over iTunes with just using hotkey combinations. Windows XP and Vista only.
iTunes Library Manager - Allows playlist export, eases moving your library from one drive to another while preserving data such as play counts. For Windows.
iTunesK1 - Gives you a graphical interface for iTunes that resembles an iPod. Mac only.
Moody - Helps you create a playlist based on your mood, works with both Windows and Mac.
MyTuneRSS - Lets you browse your playlists on your local network or over the Internet, play the songs right in your browser via a Flash player. For Mac & Windows.
Tangerine! - Software that will analyze your library noting each song's BPM (Beats Per Minute) and then create playlists based on that. Mac only.
TunesTEXT - If you have the lyrics stored with your songs, this Mac widget will display them. If you don't have them, the widget will search online databases for them.
You Control: Tunes - Lets you control iTunes from the menu bar so you don't have to switch applications, customize your menus to suit your needs. Mac only.
FoxyTunes - A Firefox extension that gives you control over your iTunes directly from your browser window.
My iTunes Widgets - Three different tools to display on your website in various configurations. Show off your purchases, reviews, or your favorites.
MyTunes For iTunes - A Facebook app to show your friends what you are currently listening to.
SimplifyMedia.com - Listen to your own iTunes library from work, home or anywhere so long as your main computer is on, allowing you to not have to copy your music to multiple computers. Works with Mac & Windows.
iTunes Playlist - A plugin for WordPress that will display a current playlist from your iTunes at the bottom of a post.
iTunesSpy - Displays your latest-played iTunes tracks on your blog.
Plastic Tunes - Displays what's playing in your iTunes along with the artist, album and more customizable information.
WP iTunes - Display your currently-playing song on your WordPress-powered blog.
iPod DP - An iTunes remote control that looks just like a gen 5/5.5 white iPod. For Mac & Windows.
iTags - We've all gotten music files with info that doesn't display quite correctly when you load it. This widget helps you edit the meta data on your files and make sure your artists, album titles and more are all in shape. Mac & Windows compatible.
iTunes Album Browser - Tons of features, seven ways to sort your albums, add albums to your desktop for quick access and more. Windows only.
iTunes Companion - A remote control for iTunes that will display your existing album art, searches iTunes and Amazon if you're missing it. Works with Mac and Windows.
iTunes Media Player - Allows you to show/hide your iTunes, play your playlists, set to shuffle/repeat and more. Windows only.
iTunes miniRate - A widget that allows you to rate your songs using the five-star scale on the fly. For Mac and Windows.
iTunes MultiAlarm - Turns your iTunes into an alarm clock. Works with Mac and Windows.
iTunes Popup - Stays hidden most of the time and only pops up when a new song begins to show you the track and a thumbnail of the album cover. Windows only. (via)