Comon sense
Why not go look at music stores and also at the tons of repetoire lists available on the internet? There are tons of pieces that we could recommend, and tons more we may not but are prefectly wonderful pieces. A piece you play now is also a great suggestion. After all, a piece you know, that you you are good at, and that you like is much better than a piece you dont know, have just learned, and maybe don't like. If the grad schools want you to be able to play a certain piece, they'll tell you that. What they want is a piece that showcases your abilities and talents, and makes you look good. So find one that fits that.