As already mentioned the Cantus CDs are very good. They are available from Stereophile. I think "Let your voice be heard" is the one I like best. I'll have to look when I get home.
I've also heard the ARC Choir, I don't know why, but I hate it. I do know a number of people that like it though...
I've also heard the ARC Choir, I don't know why, but I hate it. I do know a number of people that like it though...