It is purely a personal nostalgic preference, but Dune.
His role as Suder in Star Trek: Voyager
Cuckoo’s Nest used to be my favorite movie until (surprise) LOTR. But I liked Dourif best in Fringe.
Deadwood S1 with the preacher kills me. I cry every time I watch it. I was glad it ended when the series ended when it did, because I couldn’t honestly handle watching Doc die.