And, why do we do this to ourselves?
I have two copies of:
The Adventures of Huckleberry Finn by Mark Twain
Small Island by Andrea Levy
Thinking Clearly by Jill Leblanc
These are due to integration between my partner's books and my own.
The God of Small Things by Arundhati Roy
No Logo by Naomi Klein
Island by Aldous Huxley
These are because they are some of my favourite books and, except for No Logo, I have one hardcover and one softcover edition.
I have a one book edition of The Lord of the Rings I bought over 20 years ago. Reading it can be uncomfortable for my hands, being a fairly hefty book and not the easiest to hold. To remedy this, I bought another edition that's divided into three books and also includes The Hobbit, just so it'd be easier for me to read. But because I'm a sentimental dumbass, I still occasionally pick up the older edition I've read many times, because I have affection for it. I love the green cover with a nice painting of Gandalf. Other than that, I don't think I have any book with multiple copies.