The excellent Mozart string quintets have already been mentioned (one of them, KV 406 is an arrangement of the wind serenade KV 388, but the other five are all original string quintets), but you also won't want to forget the splendid quintet for piano and winds (KV 452), which Mozart remarked at the time of writing that it was his most beautiful work to date. The piano quartets (KV 478 in G minor and KV 493 in E-flat) are also beautiful.

Please do not overlook the Shostakovich G minor Piano Quintet, Op. 57. I recently played the Schumann Op. 44, Dvorak Op. 81, and Shostakovich Op. 57 piano quintets with some friends, and I found the Shostakovich to be the most fun to play. There's some good stuff in this quintet, even though it doesn't get as much press time as works like the Brahms.

Congratulations on the new house, Chamber Nut! Hopefully you will fill it soon with many CD's