I look forward to the day that we start seeing TFiOS pop onto this list.
Oh, My favourite was probably LotF.
Mine would hae to be To Kill A Mockingbird.
So, so many. I loved Flowers for Algernon, Lord of the Flies, The Giver and To Kill a Mockingbird.
While I enjoyed To kill a mockingbird, I've never bothered to reread it.
Animal Farm on the other hand i've gone back to a couple of times and I just adore it.
It's also not technically assigned book, but we were once told to pick a book from a list and write an essay on it. I chose Elvis, Jesus and Coca Cola by Kinky Friedman which was hillarious and I've since gone on to read several of his books.