Edgard Varese - The Complete Works, v. 1
Probably most of you first heard of Edgard via Frank Zappa, who was a big fan. If you've ever listened to any of his orchestral works, from Lumpy Gravy to the Yellow Shark, you'll be at home with this record. You can certainly hear Varese's style throughout Frank's work.
This is stuff to listen to closely. At first, it can sound a bit off in the harmonic structure. But as you listen to it, you'll understand that it is meant to be dissonant in parts. In fact, the use of dissonance for longer stretches is a big way this is different from older orchestral works. As is the reliance on percussion to carry melody.
This is an earlier record (came out in 1950), so the electronic / musique concrete stuff isn't here yet. Don't let that steer you away, though.
If people like this, I'll put up some later works. Let me know.