A friend and I have been playing four hands, just dipping into the literature. Something you will hear in Carlisle and friend's recording that is essential: one must exercise care and play with delicacy, as four hands produces twice the volume, and one can get ear fatigue rapidly if the playing isn't done with a gentle touch. I was at a master class recently, they played Heitor Villa Lobos' “A folia de um bloco infantil”, and, quite frankly, used way too powerful a touch. They hit all the notes, but...
Some of the better things we've played:
Mozart Sonatas for four hands. We've just skimmed the surface of the complete four hands collection, but it's all real Mozart, composed for 4 hands, crystalline and perfect. Like all Mozart, these works are transparent and, hence, difficult.
Ravel, Ma mère l'oye, mentioned above. A beautiful piece.
Gershwin's Rhapsody in Blue (not sure who arranged it, my studio and the music is a hike from here, but it's wonderful). Plenty of riffs for both players. Runs about 30 min, though.
Saint-Saens, Le carnival des animaux, also very beautiful. Durand ed.
Faure, the Dolly Suite
Schubert: an immense literature, the F minor Fantasy mentioned above is especially nice.
Beethoven: Symphonies, we have all nine. Yes, they are a handful, but great fun to play. Really easy to play too loud with these--restraint is a must.
Topic: Virtuosic (or almost-virtuosic) piano duets