52. Card, Orson Scott. Speaker for the Dead
53. Card, Orson Scott. Xenocide
54. Card, Orson Scott. Children of the Mind
Called The Ender Saga these days, as though it was a tetralogy; this is really a stand-alone novel and a trilogy.
Ender's Game is well worthy of its
classic bookstatus (although I'm saddened to see that the cover of this edition makes no mention of the Hugo Awards; did they become unfashionable or something?).
The other three are fairly standard quality SF really; and Xenocide should probably be divided in two to make an actual tetralogy. Card asks some interesting questions about what we mean by "sentient" or "alive" or "person", but his answer is probably a bit mystical for some (and a bit atheistic for others!).