I love this song. They never play this live though. I read an interview with Adrian Smith and he talked about how he and Bruce enjoyed making and playing the song, but it just wasn't working as a live track. Too bad, it's a fierce song.
This is tough because they're all "standard" to any Maiden fan. But I love the question. My votes go to:
From Here to Eternity
The Duelists (Love the "dueling" guitar wankery in the middle of the song)
Transylvania
The Mercenary
Paschendale
I can keep going, but these are just a few I have never seen live. I think that's what you were going for. Paschendale is on Dance of Death, which I think is an underrated album.