2001

First read this as a kid, have read it a few times since. Both the movie and this novel were collaborations between Clarke and Kubrick, covered in the introduction. What I only found out this year was there is another book, The Lost Worlds of 2001, which covers this in 240 pages of detail (including the Sentinel short story and more!). You can guess what I am reading now :)

The story in the book is very slightly different than the film, especially at the end. Both are excellent in their own way, of course. I wish the book had picked up on the lip-reading trick - in general, it feels like the film deals with HAL in more depth than the book.

While I've read this book multiple times, I think I've only read 2010 once - and I've not read any of the further sequels, though they are rated much lower.