You know, the books where you end up reminiscing about one night with friends and everyone has read them.
(I appreciate I am generalising heavily about boy and girl books, apologies. Just had a bit of a sad moment when I realised that having no girls I am less likely to pass these stories on to my children)
Swallows & Amazons, Just William, Jennings, Biggles are examples of books I plan to introduce to both my DS and my DD. And then, when they're older, maybe the Lone Pine series, although I think it's out of print now. Oh, and what about The Silver Sword (Ian Serrailer - sp)?
And YY to Little House on the Prairie, Anne of Green Gables for any child who will sit still long enough to listen to them/read them themselves. Also the Ramona books and the Chalet School series.
If your ds likes detective stories, he might enjoy Emil and the Detectives by Erich Kaestner. Originally written in German and published in 1929, it is about a boy whose money is stolen on a train en route to Berlin and who enlists the help of a group of Berlin children in a hunt to find the thief. The story has been filmed a few times. My dd really likes his children's books eg also "The Double Lottie" and I don't know the English title but maybe "the Flying Classroom"
Following on from Willard Price, what about Gerald Durrell? Not just My Family and Other Animals. Three Singles to Adventure, The Drunken Forest, Beasts in My Belfry etc all fired me up as a child (and I still love them) - and they're as unisex as they come IMO.