Try Saint-Saens Symphony #3 "The Organ Symphony"
Rachmaninoff "Symphonic Dances"
Bartok "Concerto for Orchestra"
Berg "Lulu"*
*I'm kidding about the Berg. Sounds like noise to most people. It's the kind of CD you put on just to watch people's faces when you pretend to like it. I don't know what's in the libretto for this opera, but it sounds like a visit to the dentist's office. However -- when you reach the point where you can listen to anything by Schoenberg, Webern, or Berg, with a straight face, and it actually makes some sort of musical sense to you, then you know you're truly arrived. Myself, I still giggle.