I'm a classical pianist, and I like music that I can play, so most of my favorites are either for solo piano or are piano concertos.
I'm a great fan of Rachmaninov. His preludes and etudes are fairly sublime. The piano concertos no. 2 and 3 are great pieces, I played the second one last year. As far as piano concertos go, I like Grieg, Schumann, Brahms, Shostakovich, the aforementioned Rachmaninov, Prokofiev, Tchaikovsky, and Beethoven.
Ravel's music is also some of my favorite. Gaspard de la Nuit and J'eux Deau are two of my favorite pieces, both to play and to listen to. Pretty good concerto, as well.
To find a grander piece than Jupiter, you need go no further than Mars. However, I'd put my vote in for the 18th variation of Rachmaninov's Rhapsody on a Theme by Paganini (you know, the famous one) for its seat among the grandest pieces.