I think my favourite of hers was "The Tricksters", but I haven't found a copy of it in many years.

I started with "The Changeover", and am still in love with it.
-: It's a fairly young one, though not nearly as young as "The Haunting". Young YA, I guess.
+: It survived at least two rereads as an adult, so it's not just my tasteless teenage self saying this.

I most recently read "Alchemy" and liked it quite a lot, but not with the deep love I have for the other two books mentioned.