I don't really listen to nightwish much these days, but i remember that i used to enjoy "Crimson Tide/Deep Blue Sea" quite a lot back in the day - http://www.youtube.com/watch?v=gb4QLMfOJTg.

I just love last of the wilds - nightwish, or the silent enigma - anathema I simply cannot choose only one

Metallica-Orion
Cliff Burton (R.I.P) is responsible for the ultimate bass work on this one.

Hammerfall-In Memoriam

Carcass - Genital Grinder

Metallica - The Call of Ktulu and Sepultura - Inquisition Symphony. The latter doesn't get much attention, but I love it.

Moonsorrow - Tyven

Binge and Grab (Instrumental version) by Buckethead, also my favourite song of all time.

It would probably be between Wigrid's Die Asche Eines Lebens, Emperor's The Wanderer, Hammerfall's In Memoriam or Drudkh's Glare of Autumn. Just love the sad feeling they have... too much great instrumentals out there, even without mentionning all the awesome intros (Tyven, Frost, Black Moon Overture...)

Agalloch - A Celebration For The Death Of Man
I know it's only a few chords repeated for 2 minutes, but it has a great feel to it. Also, I never get bored of playing it on guitar.

"Into The Lungs Of Hell" by Megadeth

Orion, Metallica
Thrash Attack, Destruction

Pelican. all of it, every single song.

Nargaroth's "Nargaroth":
The essence of black metal comes alive in this fiery-with-heathen-pride instrumental.

Arcturus - Ad Astra. There are some lyrics near the end but it's basically an instrumental. And a masterpiece.

I can't really choose, so I'll just post my top ten (in no particular order):

1. Dyrad of the Woods - Pain of Salvation (It's a very lush and lovely acoustic number, one of my faves from Remedy Lane)

2. Altered Course - ISIS (Very repetitive song, but that's part of it's beauty. It's very hypnotic straight through to the end)

3. Odal - Agalloch (The guitar melodies in this song and the drum march near the end are spellbinding. I also love the piano ending a lot)

4. Genghis Khan - Iron Maiden (The galloping feel and the soaring twin guitar solo at the end really make this song amazing, a favorite of mine from Killers)

5. Inside the City of Glass - Katatonia (Ends my favorite album from them (Viva Emptiness) on a very doomy note, it's pretty haunting to say the least)

6. Epilogue - Opeth (Very soulful and Pink Floydian end to an album as brutal as My Arms, Your Hearse. This song is very emotionally powerful)

7. Nattestid IV - Taake (Starts off with your typical black metal blast beats, but goes into a strongly folk-like rhythm that really makes the song shine)

8. Not Saved - Ulver (I love the bells and the piano in this particular song, it's very experimental with some static noises and all that , yet still beautiful as well)

9. The First Snow - Drudkh (Another repetitive song, yet it's absolutely bone-chilling and haunting at the same time, the 9:12 fly by quickly)

10. A Walk Beyond Utter Darkness - Xasthur (Another very haunting song where the melodies are able to seep through all the distortion and chaos)

Added "Orion" by Metallica to the list of my favorites