I'd recommend 'The Giver' by Lois Lowry. It offers a unique sci-fi perspective and raises thought-provoking questions. Also, 'The Mysterious Benedict Society' by Trenton Lee Stewart is a fun read with mysterious elements and cool technology.
There are many great options. 'A Wrinkle in Time' by Madeleine L'Engle is a classic that kids love. It has time travel and adventure.
One popular choice is 'The Wonderful Flight to the Mushroom Planet' by Eleanor Cameron. It's full of imagination and excitement. Another is 'The City of Ember' by Jeanne DuPrau, which presents a post-apocalyptic world for kids to explore.