Oldies but goldies

This time we are interested in old genre books (science fiction, fantasy, horror, etc) that have become classics or that you personally enjoy. Note that there's no hard cut-off date for categorising a book as "old": It's up to you to decide on that. But whatever your choice you are cordially invited to present one or more books to the group!

Afterwards we will have a casual and friendly chat about the books, about the subject of old books, and wherever else the conversation takes us!

You are of course welcome to bring the books you want to discuss, but it's also fine if you don't.