
Little builders are eager to experiment with new materials to create playscapes and structures. Architecturally inclined kids will love these toys that emphasize construction and open-ended play.
1. Habitadule ($69.99, Hearth Song)
2. Magna-Tiles ($49.95-129.95, Lakeshore Learning)
3. Quadrilla Twist and Rail Set ($149.95, Fat Brain Toys)
4. Tobbles ($25, MOMA Store)
5. 4D Cityscape New York City, London, and Paris Puzzle Set ($99.95, Metropolitan Museum of Art Store)
6. Tegu Mahogany Explorer Set ($125, Tegu)
7. Nanoblock Empire State Building ($47.50, The Future Perfect)
8. Modular Tree House ($88, Etsy seller Manzanita Kids)
9. 3D Puzzle Fairytale Castle ($12.50, Muji)
10. Recycled Paper Building Kit ($39.98, Magic Cabin)

Sprout Side Table
I like the marble run toy above. It looks really nice and well constructed--as opposed to the plastic ones I've seen before. I checked and found it on Amazon for cheaper, FYI, if anyone else plans to get it.
Haba marble runs are great too, plus they're more open-ended and emphasize designing your own runs. You can get a basic set of tracks and curves and add on different pieces.
You didn't mention my son's new favorite building toy, zoobs. There are 5 different connectors but you can put them together 20 different ways so you can build some really great stuff with a small set.