My mom sent me this post from Adult Swim's web site about covers of classic movie and TV show themes found on the internet. The whole article is worth a read and listen, but here's a sample for you headbangers:
Back to the Future
The soaring progressions of the Back to the Future theme (performed by someone calling himself russfuckingallen) lend themselves perfectly to a power metal interpretation. The instruments are clearly programmed, which makes me hope that someone (hopefully Blind Guardian and not Dragonforce) covers it live, but it's still a fun listen. Favorite YouTuber comment: "eardrums? where we're going, we don't need eardrums."
Secret Chief 3's cover is more imaginative, but I like how this guy CeatBeat arranged it, despite his silly accompanying video. Still easily the best theme that a director ever wrote for his own movie.