This AppleScript enables simple tweeting of iTunes' current playing track for free.
Installation is a breeze - simply download and expand the TwiTunes.scpt.zip file, and drop it into the /Users/username/Library/iTunes/scripts/ folder. If you don't have this folder yet, don't worry - you can create it easily. However, it's important to note that the script will need your Twitter password in order to post to your account. It will look for this information in your Keychain. If you haven't done so already, make sure to log in to Twitter and save your password to your Keychain when prompted.
That being said, it's important to use TwiTunes responsibly. As with any communications technology, Twitter can quickly become overwhelming if you overdo it. So make sure to only share the truly standout tracks with your followers - the ones that will really blow their minds!