Mary's instructions for searching here will find you quite a lot of material: try searches for child #26, twa corbies, and three ravens. "Twa Corbies" isn't necessarily the same song, but it is generally considered to be related; certainly, Child grouped them together.
BR>In case you don't know how to find the site Bruce mentions, here are a couple of useful links for you:
You might also have a look at The Traditional Ballad Index -do a search for three ravens.
By the way, it's usually a good idea not to start two separate threads on the same subject; makes things unnecessarily complicated!
Malcolm