This might be a stupid answer (I have no dc) so bear with me But on the iPad/iPhone there's a game called Take it Easy and you basically have to match up tubes to form a maze of different colours? Lots of different levels
You can get books of picture puzzles, like very early non-verbal reasoning, but there might be reading involved in the instructions for each question.
Usually when people ask for suggestions in this section of the forum, I think back to what we did with DS2. However, he had taught himself to read by that age (unavoidable as his older brother was in Reception and learning phonics) so we didn't have the restriction of avoiding letters.
DS2 is now 11 and still enjoys making mazes from Lego and creating elaborate marble runs. He also likes the computer game Antichamber (based on non-Euclidian geometry) and solving virtual Rubik's cubes in more than 3 dimensions.
Could you start some simple chess? Maybe start with some pawns and then introduce games with one other type of piece too?
Draughts is another good strategy game that doesn't require reading.
He loves mazes, marble runs, word searches, suduko.
Also, Where's Wally books, and all the spin off books. He has found a whole section in the library with Sword Quest etc.
He's now really mad about the Beano. Also does his older brother's non verbal reasoning tests.
And, I have just discovered that his way of mental processing is great for reading music. He picked up his brother's piano book a few weeks ago, and taught himself the entire book in less than a week. I spoke to the piano teacher who agreed to try him out, even though he's only year 1, and 4 lessons later, he's half way through book 2.
My 3 year old loves playing with Numicon and will play with it for hours. They use it in Nursery and reception I think and my 6 year old loves playing schools with it. I have learned a lot about how maths is taught at school, but mainly they just enjoy it.
Print free mazes off the internet? Playing about with Junior Meccano/lego? My DS went through a mad-crazy jigsaw phase at about 3/4 which ended with 150 piece jigsaws giving me 2 hours rest every afternoon (highly recommended!). There's a game called Rush Hour where you have to move cars about to get a little red car out (hard to explain, but a harder version of those annoying sliding tile games which make a picture). Usbourne have a series of books called Puzzle Something (school, castle etc.). There's a story and each page has a puzzle and where's wally-esque things to find. On the citv website there used to be a hamster tunnel maze type game with an around the world theme. Can't remember exactly, but DS was very into it for a while during his preschool year.