I have played many classic games in my time and they all have something that seems to be lacking in a lot of today's video games: memorable music.
I would have to say, hands down, that Super Mario has the best theme song of all time. It's a tune that easily gets stuck in my head and is sort of "feel good" music, in my opinion. Every time I hear it I remember sitting with my mom on the floor in front of the television when I was young, innocently competing with her for who can last the longest. Every now and then we still opt for the Super Nintendo over the newer consoles just to recall the good times we always had playing it.
Another video game that deserves recognition for a great classic theme song is Sonic the Hedgehog. The music fits the game perfectly and is another song that's hard to get out of your head. Yet again, the music brings back memories of my cousin and I playing video games together. I haven't talked to him in a long time so it's nice to remember those times when we used to be inseparable.
I think the best theme music is dependent on what it means to you. Memories are connected with each of the old games I used to play and though those songs probably don't mean much to others, they mean a lot to me because they remind me of my childhood.