My favorite song changes depending on the mood i'm in. If I'm angry, then something a bit heavier, like Master Of Puppets by Metallica would be ideal. If I'm in an apathetic mood, maybe Street Spirit by Radiohead. But I would have to say my favorite song of all time is... Cowboys From Hell by Pantera. Now I know most people out there won't agree on this one, but the sheer power of the song makes it a classic for me, and it never fails to get me going.