Yes to Usborne lift the flap books, a child's atlas was also popular, also a child's book about space with photographs instead of drawings.
We have some Orchard Toys games, but it's a board game set by HABA that gets the most play (and I like that it's one big box, not ten). He might also like one of the balancing tabletop games, or a set of balancing scales.
A good quality building toy, with enough pieces for big constructions. We had magnetic tiles, duplo, and wooden blocks at that age, all of which were well-used.
For stocking bits, a small retractable tape measure (the sewing ones are cheap), a small torch, a magnifying glass, magnetic letters for the fridge. A set of hexagonal fridge magnets was so popular for pattern making we had to buy a second set so we have some to actually stick papers up. A hand counter/clicker counter, a cheap stopwatch, and 'magnet men' are on my list of possible stocking stuffers this year (aged 4.5). Detailed plastic animal figurines are also good for stockings.