Considering that it's your birthday and this is a song I cannot stop listening to since I've heard it:
The Mean Greens - Operation Birthday:
Be warned there is some voice in it but I like to think the voice is more comparable to an instrument as there's no line in the song that isn't reused.
Edit:
May I also suggest the Minerva: Metastasis soundtrack. It's an obscure mod by a guy who's now working with Valve but the music is by a person named Zhaytee.
Liberalitas:
Absconditus:
Omnia:
Duco Ergo Sum:
