Obviously, if you like Mozart’s Piano Concerto No. 9, you should check out his others. He wrote 27 in all, and the later ones (at least those numbered in the 20s) are some of the best music he ever wrote—though I couldn’t offhand tell you which one is most in the vein of 9. From there, look into his symphonies, his concertos for other instruments, etc. etc.
The Archduke was my introduction to, and still my favorite, piano trio, and it led me to seek out other examples of the genre. The Piano Trios by Schubert or Brahms might be a good starting place, but there are other good ones out there, especially if you include piano quartets and quintets, such as those by Schubert and Schumann. Beethoven wrote other piano trios, of which the most famous after the Archduke seems to be the “Ghost” (Op. 70 No. 1); and check out his Triple Concerto, for piano/violin/cello and orchestra.