The anime adaptation of Attack on Titan (Shingeki no Kyojin in Japanese) debuted early this April, and it has a powerful opening. Users of the Japanese website Nico Nico Douga jumped on it immediately and made crazy awesome remixes.
Some of these mix the opening song (on top) with other anime intros or with other various videos. Some are just extremely funny.
Have a look
Shingeki no Kyojin 進撃の巨人 - OPENING HD [YouTube]