There is a thread for book reviews, but I'd like to start one on books that have been read multiple times because you enjoyed them (not because, say, you were required to do so for school or work...) You don't have to list more than one at a time; especially if you want to give some background about why you first read the book(s) and why you continued to keep on reading them.
The first ones that I can remember were the Lord of the Rings trilogy (Ace Paperback Editions). I had mail-ordered them as soon as they came out in 1965 - I was in high school in Nebraska at the time (my dad was in the Navy and had been talked into recruiting, so the family moved from San Diego to there). Although that edition was 'unauthorized', in fact there was no 'legitimate' paper back edition available in the US, and the US publisher Houghton Mifflin had goofed in printing too many of the hardbacks, which caused a legal loophole that Ace used to legally publish their edition. I later bought the Ballantine edition when it came out, but have always been disappointed in the covers.
In fact, Humphrey Carter, in Tolkien’s official biography, noted that while Tolkien was displeased with the Ace editions, they at least sported covers that resembled their stories; by contrast, Tolkien was distressed at the cover art for the Ballantine editions, to which he noted: “What has it got to do with the story? Where is this place? Why emus? And what is the thing in the foreground with pink bulbs?”
Just look at these...
The Ace editions are undoubtedly the reason why Tolkien became a big thing in the USA; they sold an awful lot of those before JRRT, Houghton Mifflin and Ballantine could agree on the contents of an edition (along with the pricing).
I had always enjoyed science fiction, fantasy, and history - and the LotR trilogy was the epic fantasy that really struck a chord with me that I read the books several times during that first year (yes, including the appendices.)