Looking for some Classical help - sheet music for piano.

So I got my wife an electric piano this Xmas. Should have done that earlier. I didn't know!

So now I want to get her more sheet music. This being the first regular access to one in some time, she needs more. But I don't know classical for beans. Can you make some suggestions?

She likes her music pretty dark. Here's what she has: (browsing)
Chopin 33 classics
more Chopin.....
hmm, she really likes Chopin I guess
Mozart, but hardly any (answering my own question I think)

Any suggestions for specific collections, arrangements or books? Some other composers perhaps?

Thank you.

not much knowledge of classical music, but try Liszt, Schumann, Wagner, Debussy. You may even be able to download sheet music off internet for her to try or check out your local library.