Puzzles are the big thing. We started about six months ago with some 24 piece ones (Cars, Spiderman, etc.) but he had them mapped out pretty quick so we tried a 48 piece puzzle. Now he's up to 100 piece puzzles that are ocean-scapes with fish and turtles and coral and dolphins, and he even has a glow in the dark dinosaur puzzle.
When he pulls out his puzzles he always starts with his wooden Thomas puzzle before assembling the big ones - since this takes so much longer, I filmed him doing the small one, just to share a little bit of his puzzle solving process with you.
He's pretty proud of himself!