Bach WTC, Beethoven sonatas, and Chopin mazurkas.
*record scratch*
Why Chopin mazurkas, you say?
Because it allows you to focus purely on musicality; this, of course, is the ideal case in any piece we play; that we are skillful enough to be able to play it however we please despite the technical difficulties.
Rarely is this the case, I find; on the contrary, we often hear all too many performances of Chopin Nocturnes and Ballades where the pianist is struggling. The mazurkas, however, allow for a low technical requirement with some truly wonderful music waiting. A true testimony to Chopin's mastery of small forms (though that doesn't take away from his larger compositions like the Ballades), and his melodic brilliance.