The Cathedral Singers have a couple of great CD’s that you may be interested in. One of them, which I have, is called “Catholic Latin Classics.” It’s all polyphonic music, but it contains classics such as Samuel Webb’s setting of the Tantum Ergo, Franc’s setting of Panis Angelicus, Gregorio Allegri’s Adoremus In Aeternum, a couple ofAve Marias, and many other classics. The same choir has also recorded a CD of all Gregorian chants, but I can’t remember the name of it. Both of these were available on Napster a couple of years ago, so they should be available on ITunes.
If you’re into sacred polyphony, you can search ITunes for material by composers such as Palestrina, William Byrd, Gregorio Allegri, Hans Leo Hassler, and later composers such as Bach, Mozart, Edvard Grieg, Gounod, and others. Out of the later composers I mensioned, Edvard Grieg’s 8 voice setting of Ave Maris Stella is one of the most beautiful pieces of sacred polyphony I’ve ever heard, and it can be found on the “Catholic Latin Classics” CD.
Hope this helps!