and I'll unabashedly recommend that.
http://www.makeymakey.com/I don't own it, so I can't get into the nitty gritty of all of it (I had a short window of time to have someone who is currently doing a class w/ them show me stuff. And her focus was the problem solving, not the sci stuff. But, still awesome)
It *does* require a laptop to do it's coolness--but usb plug and some alligator clips and...we had maple leaves working to control the touchpad on the borrowed mac. Which was awesome. touch the top leaf, mouse moved up. touch the other leaf, clicked. it was all around neato-bandito.
I think if you used it with scratch, you could do cool stuff.
(Scratch is fun in and of itself though)
Also got to talk about squishy-cuircuits--which are cool, but, I think not so cost effective? Still fun, but, eh, I'd diy 'em. But confession is that I haven't DIYed 'em yet:
http://makezine.com/projects/squishy-circuits/No experimenting more until Buffy gets back from mermaid camp