Iwasaki Taku - "Libera me" from Hell (off the Tengen Toppa Gurren Lagann OST)
A very unique piece of music that combines an excellent piano theme with operatic singing and stylish rapping. I was pretty skeptical that it would work when I first heard it, but in the context of the show itself, it fit beautifully. I never thought rap and opera could work together so well, but it just does in this song. It may not be to everyone's tastes, but I just love it to pieces now.