Anything by the Kings Singers. I've had the pleasure of performing with them twice (music composed for them and chamber chorus). I will never forget it.
Rachmaninoff Vespers (All-Night Vigil); Robert Shaw, Telarc CD-80172.
Morten Lauridsen (Composer) is great! Sounds like it could be 16th or 17th century, but is modern. Morten is alive and well and living in Los Angeles. Get the CD "Lux Aeterna" and more on RCM#19705. Samples at Amazon.com.. Love to sing his music. The CD includes his "O Magnum Mysterium" which is the best selling piece of choral sheet music in history.