Some justifications would make this far more interesting then your average bland list thread.
Here is one of mine, I'll post others but this came to mind first,
Iter Impius by Pain of Salvation
A very beautiful, oddly tongue in cheek song. I just can't pick a flaw with it, the concept behind the performance is fantastic (it is part of a large concept album) and the song is just so dynamic and heartfelt with some brilliant musicianship. It appeals to me on every level, intellectually and emotionally.