We first saw Keva Planks at The Reuben H. Fleet Science Center in San Diego. The Keva Plank area was packed with kids (and adults) intently building their own masterpieces of architecture. They were building these amazing structures by stacking the planks. No glue and no connectors. Each plank is identical.
Then, a friend gave my son Kapla Blocks for his birthday. Each wooden block is also made of pine and is identically sized and shaped. They are intended to be stacked, and you can stack them REALLY high, depending on your design. They are all weighted the same. The blocks are certified green from renewable forests of Marine pine near the Bordeaux region of France. They are used as educational toys in France, and I bet you might find them in some Montessori schools here in the States. A model Eiffel Tower made of thousands of Kapla blocks was exhibited in 2008 in the Cité de l'Architecture in Paris. Kapla has also shown at the Louvre and at the Children's Museum of Manhattan. These toys are beautiful, practical, "green," and will capture your child's imagination for years. (I like to play with them too, I must admit!)
The Keva Planks are produced here in the US. Check out their site at:
I found Kapla Blocks on Amazon.com. Here is a link to the basic set: