If I include OP and EDs it would be impossible for me to narrow it down.
As far as themes go definitely Bardocks Solid State Scooter and Guiles Theme immediately come to mind.
@Kobra678: When I hear that Naruto track, I always think about Team 7 fighting Zabuza lol
And yeah, Needless has an epic soundtrack. Even the transitions make you wanna air guitar lol
But I would replace the Bleach theme with the one from Attack on Titan. If you've seen it, you know the one I'm talking about lol
There is seemingly no 'perfect' way to truly say goodbye. So I gathered a bunch of them!