There were some great "getting started" lists above.
After being subjected (tortured?) by college level music "appreciation" courses in my whopping one semester as a Jazz studies and music education student, and having the usual mandatory opera parts to sing, as a singer back then, and concert choral arrangements, along with being required to pick up a classical stringed instrument (note to self: Double Bass was a bad idea in a State known for snow in winter and practice rooms a quarter mile away from the dorm... Haha... But then again, I'm also stupid enough to have carried a concert Baritone horn in a marching band... Which is effing painful after six hours...), I'm impressed with the lists provided. Nice!
About all that's missing is choral stuff and it's not everyone's cup of tea.
Everything from Gregorian Chant (one really can't laugh as hard at Monty Python making fun of it, until you understand the original art form but then slamming their heads with a board for rhythm, and what that means for the use of the chants as religious behavior is some of the funniest satire based on music, ever done), to various operas and arias, to more modern stuff like John Rutter's Gloria, it's all tasty listening to me when I'm in the mood. Heck, come a little more modern and find a well done recording of Shannandoah and a great arrangement done by a really good concert chorus, or any number of interesting Shakespearean words set to various songs throughout various decades in various styles, those are all a treat too. Various arrangements of "There is no rose (of such virtue..." are stunning additions to the artistry of the words.
I have to bow my head and pay omage to the master, Leonard Bernstein's Chichester Psalms as a total pain in the butt to perform RIGHT, but also a favorite to just sit with eyes closed and hear performed right -- on either a great recording or especially live when one can find it. Many modern "pop" orchestras and choruses simply won't touch it. Too difficult, and not enough "audience appeal".
(Some of the parts in that work are a serious b**** to sing properly.)
Rutter Gloria:
http://youtu.be/uaYkpoOC3S4
And the hardest part of the work (IMHO) to perform well, done by the Cambridge Singers with read along musical score.
Rutter will jack with your head jumping back and forth from 3/4 to 5/8 time when you're first trying to sight read the bloody thing.
http://youtu.be/o2-EsLZ2iBA
Bernstein... Masterful. Amazing. He'll just kill you with unresolved dissonance for 11 minutes and then tease you with chords that start to sound nicer, then at 13:30 or so in this video when your ears want nothing more than a nice minor or major chord, he busts out one of the most beautiful choral call and response segments ever written. Still in a lovely haunting minor key...
http://youtu.be/7Yhnml4DW9g
(It helps to also look up the words for more meaningful listening to the entire work.)
And even though I made fun of "pop" orchestra, there's no doubt that the Boston Pops under Williams was an unmitigated success, and many of their works are "gateway" classical pieces that many recognize and then start listening to other pieces.
One can throw on Copeland and many folks will instantly recognize Fanfare for the Common Man...
http://youtu.be/FLMVB0B1_Ts
Or of course, Hoedown...
http://youtu.be/LsReWx9XdNs
("Beef, it's what's for dinner!")