Kano is a computer you build and code yourself. Lego simple, Raspberry Pi powerful, and hugely fun.
US$149.99, free shipping worldwide.
I really wish my kids were a bit older - this is exactly the sort of thing I cannot wait to use to introduce them to computers. Not just "computers", as such, but computing. How they work, what the components are, what can be changed, how you make them work, and how you fix them when they break.
(Found via a passing comment in Turning This Car Around - the podcast I pretend to listen to for parenting chat, but it's this nerdy shit that really gets me)