Have you ever heard Allegri's (1582-1652)"Miserere"? Thats a good one (albeit it repeats very often). Its a mix of Chant and Polyphony.
I haven't, but thanks for the recommendation. I know next to nothing about classical music, but I listen to NPR once in a while and some time ago they played chant and I was really moved by it. So I went to my local Borders listened to few CDs and decided on the Tallis Scholars, it was just what I was looking for at the time.