His Varese disc with the CSO is terrific. I also like the one Ligeti disc he has made for DG. His Ravel with the BPO is quite good too. I especially like his quick paced "Daphnis & Chloe". What it lacks in sheer sumptuousness, it makes for with pure elegance and elan. Of course, any of his Anton Webern is self recommending. His recording of the complete, 3 act "Lulu" is pretty much definitive. Then there's the entire Bartok cycle with the CSO. All of it is at least good, if not outstanding. I'm hoping that DG will put his Bartok into a nice box of some sort. On DVD, he gets high marks for his "Pelleas & Melisande" (Debussy), and I feel that his recent one of Janacek's "From The House Of The Dead" is outstanding. I'm really glad that he's been acknowledging Janacek in the last few years. If you can deal with Chereau's 19th century industrial revolution context for Wagner's "Ring", Boulez's conducting of it is pretty darn good. All of the Stravinsky discs he has made with the Cleveland Orch. are quite good too, with the exception of one slight disappointment: Petrushka/Rite Of Spring. For some reason, his latest "Rite" sounds a bit lethargic and/or didactic. His earlier Cleveland one on Columbia (Sony) is better. Go figure! And of course, Boulez conducting Boulez is the real deal.
Seriously, it's hard to go wrong with Boulez in any 20th century music.