I'm pretty sure that I have seen (somewhere) a ballad about the Halifax explosion. I forgot where I saw it. Possibly it was in an anthology of ballads from the maritimes. When I get home I'll look it up and post it.
I agree that Edmund Fitzgerald is overplayed, but I once heard a great song about the Apollo 13 disaster sung to the tune of Edmund Fitzgerald.
But I think my all time favorite is a Titanic song called "God Moves on the water" which I heard on an Alan Lomax recording of songs from the Georgia Sea Islands. It was sung by Bessie Jones and is just a real catchy number.