Jay Silver and Eric Rosenbaum, from the Lifelong Kindergarten Media Lab in MIT, make the best fun tech-toys ever. Our favourite is Makey Makey, a credit card sized PCB which allows you to control the bottom 8 keys on your keyboard plus the arrow keys by attaching almost anything which conducts electricity to your computer via the usb port. If this makes no sense to you at all, just watch the video. I was totally hooked and had ordered one within minutes of seeing it.
When it arrived all the way from joylabz in the US, it was every bit as good as in the video and more! It is now a staple on all our teacher training courses. You NEED one!
You can find more ideas on http://www.makeymakey.com.