Freegal is a service that libraries can sign up for, that allows their patrons to download a limited number (my library does 3) free songs every week. Once downloaded, the songs belong to the patrons --- forever. No fees, no deadlines, no expiration dates.
I discovered freegal on my library's website about a month ago and so far have downloaded nine songs. I'm currently working on getting the "Little Women" musical soundtrack. The website is not extremely well organized so you DO have to dig to find what you want, but they DO have a LOT of options --- there were very few musicals, for instance, that they didn't have. And they have tons of popular music too.
The music doesn't download directly to iTunes --- you have to download it, then use the iTunes function "add file to library" and select the music files from your downloads folder. It only takes a few seconds though and you can save yourself quite a bit of money this way.
So check and see if your library subscribes! If not, put in a request! Then, get the word out!