I cant just pick ONE but my top10 faveourites would have to be
Metallica - Master of Puppets
Edge of Sanity - Crimson
Nile - Unas Slayer of the Gods
Symphony X - The Oddyysey
Dissection - Where Dead Angels Lie
Pink Floyd - High Hopes
Nightingale - The Glory Days (the Nightfall Overture version)
Opeth - Wreath (I would pick Bleak over this... but with this song it relates to some really good memories
)
Decapitated - Three-Dimensional Defect
Deströyer 666 - Genesis To Genocide
Some of these would change by the month or so though...