Browsing around on Youtube recently, I came across a bunch of covers of "Scarborough Fair". Here are a few of my faves:
First up, Queensryche. Not a band I'd have pictured covering this song, but I think it's actually very good. Although when Geoff Tate gets a bit high pitched on the "SAAAAAGE!", I kind of wish he wouldn't. This version is accompanied by a fanvid featuring awesome early 90's videotape effects.
Next up, Leaves Eyes. This version is all out symphonic metal, complete with uilleann pipes. True fact: Any song can be made 17.83% more awesome with the addition of uilleann pipes.
Finally, and possibly my favorite, is My Dying Bride's version. This version uses lyrics that differ significantly from the one that Simon and Garfunkel made us all familiar with (and which Queensryche and Leaves Eyes seem to have used as the basis for their covers.) I don't know if MDB used alternate lyrics from the original folk song, or simply wrote their own. (I'm leaning towards "wrote their own", actually, since the added lyrics feel a lot more like the work of Aaron Stainthorpe than that of a medieval balladeer.)