I was fascinated with The Boxcar Children and, to a lesser extent, Surprise Island when I was a kid. My son, when he was around the same age (2nd/3rd grade?) plowed through a lot of the series.
For early readers there was (and is) a great series of three books by Ruth Stiles Gannett; the first book is titled My Father's Dragon. I haven't seen them for years, but I think they'd age pretty well.
I think, for sf, many of the classics still work well as intros to the field--better than much recent stuff, which can be off-putting. Heinlein (from before the preaching bug bites him), classic Asimov that first saw light in the 40s/50s, Clarke from the same era, Pohl/Kornbluth, Niven's "Known Space" books etc.-- my son and some of his friends plowed enthusiastically through this stuff in their teenage years, even though some of it was written generations before. Some recent stuff by John Scalzi ("Old Man's War" etc.) seems to have the same readability-without-prerequisites. I don't think he's as imaginative as the older writers (his aliens, for instance, seem to me rather weakly thought-out). But that clearly hasn't kept him from hooking a lot of readers.
On the fantasy side, I'd recommend Zelazny's original 5 Amber books (though he can be off-putting about women) and Norton's earlier Witch World books (though her somber steady tone can wear thin after a while). My kids really liked Susan Cooper's "Dark is Rising" sequence; it seems to have, not just readability but rereadability (essential for literary addiction, I think).
On intro books (though some are favorites, too)
For early readers there was (and is) a great series of three books by Ruth Stiles Gannett; the first book is titled My Father's Dragon. I haven't seen them for years, but I think they'd age pretty well.
I think, for sf, many of the classics still work well as intros to the field--better than much recent stuff, which can be off-putting. Heinlein (from before the preaching bug bites him), classic Asimov that first saw light in the 40s/50s, Clarke from the same era, Pohl/Kornbluth, Niven's "Known Space" books etc.-- my son and some of his friends plowed enthusiastically through this stuff in their teenage years, even though some of it was written generations before. Some recent stuff by John Scalzi ("Old Man's War" etc.) seems to have the same readability-without-prerequisites. I don't think he's as imaginative as the older writers (his aliens, for instance, seem to me rather weakly thought-out). But that clearly hasn't kept him from hooking a lot of readers.
On the fantasy side, I'd recommend Zelazny's original 5 Amber books (though he can be off-putting about women) and Norton's earlier Witch World books (though her somber steady tone can wear thin after a while). My kids really liked Susan Cooper's "Dark is Rising" sequence; it seems to have, not just readability but rereadability (essential for literary addiction, I think).