Young Adult fiction is my "go-to" place for this. Nearly anything that has won the Newberry Award is great for the whole family. Some standouts in my mind:
* Island of the Blue Dolphins
* Chronicles of Prydain (Book of Three, The Black Cauldron, etc)
Chronicles of Narnia aren't Newberry winners, but are good regardless (if you don't mind the religious subtext).
+1 for other people mentioning The Hobbit and Lord of the Rings.
Our whole family has enjoyed classics like Pride and Prejudice and Dracula -- such books are called "classics" for a reason.
Modern YA fiction has some very good books as well -- we all enjoyed Hole by Louis Sachar.
Some good modern sci-fi too -- Project Hail Mary by Andy Weir was well received, as was Ender's Game.
Brandon Sanderson's stuff is very good. Whole family enjoyed The Way of Kings and the books that follow.
(For context, "whole family" is mix of genders, ages 10-15)