I saw a lot of cool modern stuff for kids in Kid O while I was in NYC, but the thing that impressed me the most was this Swiss toy called Bilibo. It's just a really simple plastic shell that kids can use for all sorts of playing. You could sit in it and rock, have someone spin you around, or wear it like an over-sized helmet. The website also shows kids playing with it in a pool, using it as a turtle shell and a tunnel for toy trains. It's simple, sturdy and leaves a lot open to the imagination. I spoke with the woman working at Kid O about them and she said that you can only get them in the US through them, and that they might be distributing them to other stores in the US soon.
For now you can order one for $30 from Kid O
Also, get the general kinderspiel from Bilibo.com