The Fleetwood Mac Legacy website has 3 covers of "Songbird" available for download this week. One of them is Eva Cassidy's beautiful version. While I don't think it's quite as good as Christine's original version, I think it is excellent. You can download here. Just click on SOTW on the left side, and then right click & save target as.
http://www.fmlegacy.com/main.html