For me, currently, it is Cleopatra and Frankenstein by Coco Mellors. There is a lot of hate about this book. I don’t know why, the book for me is awesome. First few pages and I’m already hooked. Some chapters got me guessing on the relevance of it in the story but it all made sense at the end. Though it’s a debut novel by Mellors and some writing needs to be improved. Looking forward for her future books.
House of Leaves, probably.
LotR, of course.
Going Postal comes to mind.
The Ocean at the End of the Lane too.
The Great Gatsby is another.
Blood Meridian.