Music Minus One publishes sheet music for major works for solo instruments plus accompaniment, as well as chamber music, that includes audio CDs of the work performed by a full orchestra, and the same work performed by the same orchestra without the solo instrument part. Tune up your piano, rev up the CD player and play along. Their website features an online store with their full catalog, and lots of sample clips.

Part of the fun of having a digital piano is the potential for having the piano perform the accompaniment for a piece while I play the solo piano part. Ideally, this requires professionally produced song discs designed for this purpose, and while there are many such discs available for purchase, very few are anything I'd be interested in. (The E-Z Play Disney and Christmas songs are probably great for a certain demographic, but I'm not in it.) You also have to put up with the limits of the digital piano versions of other instruments, which are sometimes less than convincing. But—and this is a big but—the digital piano can have the accompaniment follow you, and wait for you to hit the right notes before proceeding. MMO on an audio CD waits for no man.

You can also use regular MIDI files, commonly found on the Internet, though they may take a little tweaking in a sequencer to play properly (i.e. muting/following the solo track).

Yamaha's Disklavier format is essentially a combination of MMO and MIDI follow-along, with recorded audio following your playing. It's only available on very expensive and well-equipped Yamaha acoustic+digital pianos, and not available for the Clavinovas.

MMO has been around for years. IIRC, they used to print stereo LPs with the solo part on the left track and the accompaniment on the right, so you can tweak your balance to hear one part, the other, or both.