There are several ND tunes that are special to me:
If Forever - I love the "cowboy" feel to the song (it almost sounds like an oldtime western tune at times), plus the lyrics are quite emotive. Paul's voice really shines on this song and it is just very different from most of their other tunes.
In The Absence of Grace - Just pure power and brutality, man. I love the hell out of this song...and the intro is KILLER!!!
Collapse of the Fallen Throe - To me, this song epitomizes ND. It has all the elements that make them so great. If someone asks me for one song that I feel sums up ND, I play Collapse for them.
RAIN!!!!! - Everything about this song is awesome., from the chugging intro to the "mellow" bridge part in the middle, to Paul's thundering vox. Just an awesome tune all around and one of my favorites.
Twilight Innocence - OK, this song brings the sappiness out in me. I think about how much I love my daughter every time I hear this song. So fucking beautiful...
Dominate The Human Strain - "WHERE HAS YOUR SAVIOR GONE TO???" I love the lyrics in this song, and the sheer brutality in it. One of ND's heaviest tunes, IMO.
The Fifth Day of March - The emotion man, the emotion!!! Nobody brings that emotional pull like Paul.
Lazarus Regret - short, heavy and to the point. I just fucking love this tune.
Those are the highlights for me so far, and I can't wait for Aphotic to add to the list!!!