Excellent suggestions. In addition, try Sacred Feast on dmp (hybrid SACD if you have a player) and the Rutter/Cambridge Singers series on Collegium, particularly Faire is the Heaven, There is Sweet Music (listen to Stanford's "The Blue Bird--you literally hold your breath as they sing it), Ave Maria and their madrigal album Flora Brought Me the Sweetest Flowers (or something like that). Shaw also recorded Schubert Songs for Male Chorus on Telarc, which is primarily unaccompanied singing, and with his old chorus there was Deep River on RCA, nice arrangements of spirituals. Finally, there are some recordings of Russian choruses which I have heard (unfortunately, I didn't get the group or label) which are terrific and worth getting if you can find them--as a bass/baritone, I only wish I could reach as low as those Russian basses!