My favorite score of his is Portrait of a Lady. Can listen to it on endless repeat...especially "Twilight Cellos" and "A Certain Light."
I really loved his classical stuff; that piano concerto linked above is just great if you haven't heard the whole thing. Orawa is a great fast-tempo string piece with relentless energy. Worth a look.
I can't link on YT at the moment, but there are plenty of clips up there.
I am very saddened by this news. I have enjoyed so many of his film scores and concert works. I join other posters above in highly recommending PAN TADEUSZ. There is also an excellent CD of four concert works on Olympia OCD 308, which includes ANGELUS, a huge-sounding work for mixed choir and orchestra that is alternately terrifying and beyond beautiful. (Avoid the pale, lackluster Naxos CD of this piece.)
A bit of trivia: Kilar wrote the fanfare played at the inauguration of Pope John Paul II. This was available on a Crystal LP.