Choral works, huh? Well, there are the usual suspects by Bach (cantatas, Passions, Mass in b-minor, etc) and Handel (Messiah, of course, but a ton of others too - there are some who believe that Theodora is his best choral work). Mozart and Haydn masses, Beethoven's two (Mass in C and Missa Solemnis) and well as a few other works, works by Elgar, Brahms, Vaughan Williams, Dvorak, Mahler and just too many to mention.
Two that I think would be interesting candidates: First, something by Berlioz - Romeo & Juliet, Damnation of Faust or the Requiem (although that really requires surround sound to do it full justice). Thinking outside the box, perhaps something like Harmonium by John Adams - very accessible for a modern work.
Guess there is always Carmina Burana......