This series along with the movies has generated a lot of really good music, and there are several CD soundtracks available.
The music for the opening and ending themes of this series was written by Japanese composer Yoko Kanno. The lyrics for this song were written by Origa and Shanti Snyder, and sung by Origa.
Origa, real name Ol'ga Vital'evna Yakovleva, is Russian but works mostly in Japan. The lyrics of this song are mostly in Russian, with some English and a little Latin. This following is the only version of the opening I could find on YouTube. Unfortunately the username of the person who uploaded it is overlayed on the entire video, which is annoying but can't be helped.
Although this post is about the music, not the show, I should point out (if you've never seen it), that the "primitive" computer animation in this opening is used only for the opening. The series itself is done in conventional animation.
Fortunately for my purposes, someone uploaded the full song to YouTube with no graphics to clutter things up, only the original lyrics accompanied by the English translation. And here it is.