Verified answer

I can't tell from your question if you are wanting creepy or demonic sounding "evil" music. Here is a piece that I consider demonic by Prokofiev from his Scythian Suite:

http://www.youtube.com/watch?v=Y4U7wNZu-CU

Here's a creepy one by Liadov "Kikimora"

http://www.youtube.com/watch?v=slGClWHC-PQ

Music cannot sound evil. Evil is a philosophical concept and music can only convey human emotion (not philosophical concepts). At best it is highly subjective as to what constitutes any one specific interpretation of a piece of music. However, I think I know the kind of thing you are talking about...

How about Scriabin's Piano Sonata No.9. op.68 "Black Mass."

The Liszt Totentanz is a good one; it incorporates the Dies Irae. If you google "Dies Irae" you'll probably come up with some good ones. There is also the Bach Toccata and Fugue in d-minor; you'll recognize it as the Dracula music.

Organ work, Piece Heroique by Cesar Franck would seem to fit...

http://www.youtube.com/watch?v=ayZBJBFCE4U