A "postwar" composer I've always liked is Bernd Alois Zimmermann. For one CD, I'd recommend Requiem für eine jungen Dichter, a massive and overpowering (though kinda depressing) vocal/tape collage piece covering 20th century history (well, through about 1970). I have a Sony recording with Gielen conducting, but I think there's at least one other. Because the tape is prominent, I wouldn't expect much difference between recordings (I saw a live performance once, and it sounded almost identical to the CD).
A Luigi Nono piece I really like (despite his Commie agitprop sensibilities ) is Como una ola de fuerza y luz, which is a totally fiery and intense piano/vocal/orchestral/tape work. I have an old Berlin Classics CD, but I'm sure the DG (and possibly others) are OK.
Warning: both of the above employ 12-tone "idiom" in places (and the composers' overall works are generally serial), if that's a no-no for you.
Big fan of Morton Feldman, though he's likely too far out for many (sparsity, silences, low volume). The works that usually get recommended to "novices" are Rothko Chapel and Coptic Light for orchestra. I personally prefer solo piano pieces like Triadic Memories, Palais de Mari or For Bunita Marcus.