Nearly all of the 4-album set “A Treasury of Gregorian Chants”. Recorded in the 50’s but nothing beats a classic.
Mozart’s Requiem, for the passion.
Berlioz’s Requiem, for the beauty.
How did the Allegri go, Malacandra? We did it last night too for Ash Wednesday. Our sops sounded great on the top Cs.
I love both of those, too – “Jerusalem” stirs my little Anglophile heart, and a few years ago I sang in the Pergolesi Stabat Mater and really loved it. (I think my favorite movement was “Fac ut ardeat cor meum.”) And I’m very fond of a lot of the stuff already mentioned in this thread (e.g. Handel’s Messiah, which I’ve wanted to sing in for years now).
Last spring I sang in Mendelssohn’s Elijah, which is spectacular – I especially loved the part about Elijah’s contest with the prophets of Baal, and even more so the part just afterwards where the choir sings “Before Him upon your faces fall!” and then comes in pianissimo with “The Lord is God!” It’s such a tremendous moment – I was always afraid I’d start to cry while singing it…
I also have a thing for English anthems (possibly a side-effect of being a student of the English Renaissance!) – I think my favorite may be Farrant’s “Lord, for thy tender mercy’s sake,” which is a very simple, moving little piece. And I love Byrd’s “Ave Verum Corpus” – possibly my favorite setting of that text. And Batten’s “O Sing Joyfully”…
Oh, there’s just too much good stuff – I also want to put in a good word for the works of Benjamin Britten, and also for the medieval hymn “Angelus ad virginem” (best known now for having been mentioned by Chaucer, in the Miller’s Tale of all places…)
Well, I was in choir when I was in college, so:
This Christmastide (Jessye’s Carol) is a favorite.
Alleluia, in a setting by Ralph Manuel. A previous director of the St. Olaf Choir once said that when you sing an Alleluia, it’s like you’re dipping into an endless, eternal river of praise…
Haleluya! Pelo Tsa Rona, Freedom is Coming, and Singabahambayo, from a book of South African songs of praise. Simple, yet fun to sing and listen to.
Ah, but did I mention that it was the St. Olaf Choir? Which means, the choral works of F. Melius Christiansen. These are the ones that most stick in my memory:
O Day Full of Grace
Beautiful Savior
Psalm 50
Praise to the Lord
Betty White would kiss you for that! 
Our local classical station, WCPE (which is available on the Internet, by the way) carries a program produced by St. Olaf’s and featuring their choir every Sunday morning.
Is she a singer? composer?
Her character on the Golden Girls was from the (fictional?) town of St. Olaf, Minnesota. Her St. Olaf stories were legendary…
Another movie reference from me- Non Nobis Domine from Kenneth Branagh’s Henry V.
Betty herself (who is a brilliant and compassionate woman) attended St. Olaf’s or was close to someone who did, and used it as a gimmick for her flutterbrained “Rose” character. The first “St. Olaf’s” stories were adlibbed by her, and it became something that was written into the scripts, the actual credited scriptwriters collaborating with her on what would come out funniest.
Oh, I knew there was a St. Olaf’s College. I almost applied there, but my inner Golden Girls fan eventually saw the light and realized I’d have to spend at least four winters in the middle of Absolutely Nowhere Near Civilization, Minnesota, and quieted down…
The words are by Isaac Watts. I don’t know of any actual tunes he wrote.
There’s some confusion, I think, because the poems are themselves called “hymns” and so Watts is a hymnodist, but we also call the songs “hymns.” If you look at the hymns you like that have words by Isaac Watts, I bet you’ll find the tune has a different composer.