I buy quite a lot of secondhand classical LPs because they're cheap but sometimes I forget what I actually own. A few months ago I saw the Asko|Schönberg perform Bartók's Sonata for Two Pianos and Percussion at the Muziekgebouw and I absolutely loved it but I couldn't find a recording particularly easily. Cue me looking at my LPs this weekend, and it turns out I own a recording of it! It's the B-side to a recording of Bartók's Piano Concerto No.2, played by György Sándor. I have a few Bartók recordings by him and they're all insanely good. The Sonata is played by him, Rolf Reinhardt (piano) and Otto Schad and Richard Sohm (both percussionists). Unfortunately I can't find this recording on youtube, but here's another a nice one:
Béla Bartók - Sonata for Two Pianos and Percussion, part III Allegro non troppo
The work consists of three movements: I Assai lento - allegro troppo, II Lento, ma non troppo and the third that I posted above. Bartók wrote it in 1937 and was himself one of the pianist playing at the premiere. It's a piece that has everything I love about Bartók, it's rhythmically exciting, there's some beautiful folk-like melodies, but there's also a lot of moments where you have to pay proper attention to know what's going on. The third movement is probably the most memorable because of the theme played by the xylophone, but it's also the most boisterous (not a bad thing). If you like it you should listen to the entire thing, here's Movement 1 and here's Movement 2 (and 3 again).
Other YPGTCM posts on Bartók: The Miraculous Mandarin and Violin Concerto No.2.