'Old and Wise'-Alan Parsons Project

This one is based on the real Rurouni Kenshin series, not the made-for-TV anime series. The one they called 'Samurai X,' I believe. It's a very somber song, and since the series itself is a fairly sad one as it is, it goes along very well.

'In Nomine...'-Adagio

This one's based on Devil May Cry, the anime. Since the song is very high-energy, it suits the action scenes portrayed quite well.

I'll add as I find ones that tickle my fancy. Note that most of what I find will be Rock or Metal in nature, so if it's not your thing, you don't have to watch it.

However, if you have some of your own that aren't Elfen Lied related that you'd like to contribute, feel free to post them in this thread and I will watch them, review them, and add them to the list with my opinion.