Here are just a few that you should learn:
Six Ecoissaises by Beethoven - this is a much more light-hearted piece than his other works.
Sonata in G major - Haydn
Sonata in C major - Haydn
Sonata in D major - Haydn ( I am a bit of a Haydn fanatic...mayb because most of his stuff is cheerful)
Any of Bach's Two Part Inventions...they are hard enough to learn on the technical side of things.
I like his Two Part Invention in A minor
Traumerie by Schumann - this is as slow soft piece and is widely known.
Waltz in a flat by Brahms (i think that is the name of it...it is his most famous piece anyway!)
Chopin's Nocturne in C minor.
Fur Elise by Beethoven (everybody thinks this is an easy piece but most people have only ever learnt to play the intro. The full piece is quite challenging!)
Moonlight Sonata by Beethoven
Dance of the Sugar Plum fairy by Tchaikovsky (This sounds really nice on piano)
Morning by Edvard Grieg ( this is very nice too and has recieved huge recognition)
Sonata in E flat Major K282, second movement, Menuetto I and II by Mozart
Mazurca in A minor by Chopin
I hope that this helps...These are some of my favourite pieces by these composers. I have been playing piano for nine years too!
Anyway...you should try something that isn't actually classical like film scores. The harry potter film score sounds amazing on piano especially Fawkes the Phoenix! I LOVE John Williams. Here is a link to it: http://www.youtube.com/watch?v=WHIHqZyK9rI