Symphonic is a dashboard widget that allows you to simply type in a song name or artist name and voila, iTunes does its thing. It works great, say, when writing a proposal and you just have to quickly hear Dig For Fire or your brain will explode.
If random play is also turned on, you have a system that will continuously feed music into which you can quickly inject requests with minimal effort.
[robg adds: This is a pretty handy widget; it has some other inquiry and search modes as well -- be sure to read the Help Page for info on the various modes and search abilities...]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20050728001804284