American Composers such as Carter Pann, Robert Rollin, Michael Colgrass and the likes.You could possibly also play Francois Rosse(french composer).
Bartók Microkosmos is just wonderful. Its a progressive difficulty set of some 150 pieces ordered in six books, from very easy to pretty difficult (book 6).Schönberg little pieces Op 19 are also beautiful, short and (relatively) not very difficult to play. I think they are a good first approach to Schonberg's music.What's your piano level? What works are you playing now? That would be a better staring point to better recommend you pieces