Hmm... If I wanted, there would be nothing but Maiden on this list. But I'll try to be varied.
0. Iron Maiden - Hallowed Be Thy Name: Hallowed Be Thy Name is the god (no pun intended). It's untouchable. Hence, it earns "0" place. It is my favourite Maiden song and IMO the best song ever written. I don't care if it's "mainstream" or "popular" (I don't know if it is, but I would assume that it's quite popular among Maiden fans), it's still brilliant.
Then on to the actual list. Hallowed Be Thy Name is not on the list, it's miles above it. However, that might be a bit hard to show on a computer screen, and I don't want to face any lawsuits for strained scroll fingers
1.
Iron Maiden - Quite A Lot Of Good Songs With Intelligent (or otherwise good)
Lyrics. I could insert Fortunes of War, the Aftermath, Paschendale, The Legacy, For the Greater Good of God, Brighter Than A Thousand Songs, Brave New World, 2 Minutes to Midnight, Rime of the Ancient Mariner, Blood on the World's Hands, Look for the Truth, Judgement of Heaven, etc. etc. etc. All of those I consider to be extremely good songs even without the lyrics. However, a song can't reach number 1 on this list without also having intelligent lyrics, IMO. Eg. many songs (Prowler, Bring Your Daughter, etc.) have pretty good tunes, but they lose out to a lot of songs because I find their lyrics or themes disturbing or otherwise inappropriate.
2.
Black Sabbath - Paranoid - Yes, yes, I know, a popular song, but it's just amazing. I don't know what it is with that song, but it just grabs me every time. Hell, I don't even know the lyrics, but it still is amazing.
3.
Iced Earth - The Gettysburg trilogy. At the moment, I would have to say my favourite from them is Hold At All Costs. Yes, the lyrics are slightly cheesy, but I still find these very good songs.
4.
Guns 'N Roses - Civil War - A great song from a great band. The lyrics are intelligent and thoughtful, which is an important factor with me. Welcome to the Jungle and Sweet Child 'O Mine are perhaps better musically, but the lyrics raise Civil War over them.
5.
Metallica - Quite a lot of early/mid stuff (up to the black album). Hard to say, as I've only recently properly discovered early Metallica (before that I had a lot from Load
and I didn't really appreciate them). At the moment, it's gotta be One, Master of Puppets, The Unforgiven, Ride the Lightning, For Whom the Bell Tolls, or Seek and Destroy.
Honorable mentions:
Guns N Roses - Sweet Child 'O Mine, Welcome to the Jungle - Both great songs, some of my earliest experiences with hard rock/metal.
Deep Purple - Smoke on the Water - Arguably the song that got me into metal and hard rock in the first place. Not that much of a favorite nowadays, but it deserves a mention.
Iron Maiden - Aces High - The first Maiden song I ever heard.
Judas Priest - Another early song for me. It's great, nothing more to say.
AC/DC - Thunderstruck - It would have been number 6 for me... Though technically not metal.