Final Fantasy IX is my favorite video game. It is the only Final Fantasy game I've been able to reach the end of, and I've done so many many times. For me, I can easily pickup this game whenever and run all the way through it without getting sick of it.
The Art of Final Fantasy IX. It's full of gorgeous development artwork for a variety of characters, monsters, and environments. And of course, it has a bunch of Amano pieces in it as well. Overall, you can tell there was tons more that they left out and so it's a little upsetting to see they didn't add more into the final product, but it's still one of my most treasured art books.