Brothers in Arms would make a nice instrumental.
Why Worry also as proved by Chet Atkins.
Well, also Metroland is pretty melodic, but the problem here is the whole melody is just too short! It's going for less than 30 seconds, so it couldn't be a song that I would call truly melodic. Its strong parts are Mark's delivery, emotion, amazing guitar playing, perfect recording quality, fine musicianship, and catchy lyrics. In other words, anything but melody, hence my opinion.
Brothers In Arms and Why Worry are good ones, yeah. Still can't put it on one level with famous melodies though. What makes Brothers In Arms work is Mark's whispering vocals and the out-of-world guitar playing which compliments the vocals perfectly. I remember Joan Baez's cover of Brothers In Arms, and how it sounds strange because it lacks the lead guitar, which ruins the whole thing in my opinion.
You see, this is the "problem" with Mark's songs. You take something out, and suddenly it's a completely different song, never standing a chance to compare with the original, even sung by great singers. And the melody has nothing to do with it. But think of something like "Fell Like Going Home", now that's a melody!