What are the symbols of the conflict between good and evil in the novel?I have the houses already of course but what else is there?

I really don't think that Wuthering Heights is about the struggle between good and evil. 

Although Heathcliff is pretty darn nasty, it's hard to see him as evil incarnate; he's more a case of a person overcome by obsessive love and jealousy.

Catherine (the elder) is certainly no saint with her two-timing of Heathcliff and Linton.  Edgar Linton is a decent fellow, but a whiner, at least in his youth.  Catherine (the daughter) is at times deliberately cruel to Hareton.  Her cousin, Linton Heathcliff, is a pathetic crybaby who is an accomplice to Heathcliff's plot to kidnap Catherine and Nelly.

The only character whom I truly admire is Nelly.  She is caring, loyal, and intelligent.

I suppose you can look at Wuthering Heights as a symbol of evil and Thrushcross Grange as a symbol of good.  I, however, would prefer to see them as symbols of decay and civilization, respectively.