Erkki-Sven Tuur: Architectonics I-VII ("music should arouse questions with which people generally do not like to be concerned"). Progressive, atonal AND tonal....amazing. I've had this disc for about three years and STILL hear new stuff going on.
Arvo Part: Tabula Rasa, Fratres, Festina Lente, Summa, Alina, Cantus for B. Britten, Trisagion, Symphony #3, and more. His tintinnabulation technique makes time stand still, but is totally engaging. I can't relax with his music, it's intense in its simplicity.