Using Yahoo! webservices, you can interface your iTunes library to the Yahoo! Music Search and fetch any missing information for your library items. I have a lot of songs with missing tags, such as album or release date. Using Ruby and a simple REST query, combined with an AppleScript, you can use a hot key in Quicksilver to quickly load in of the missing information. You'll need your own Yahoo! API key from Yahoo Developer. The code is a little long, but you can see the listing on my blog. [robg adds: I haven't tested this one.]

	Read more at MacOsxHints
	feeds.macosxhints.com/~r/macosxhints/recent/~3/136879489/article.php