These are some resources and ideas for things we've done with the Makey Makey. (about $45) Check out more photos of students using Makey Makey in STEM class from Spring 2015! A new / smaller / less expensive "Makey Makey Go" ($19) is available via Kickstarter through 7/10/2015. (estimated delivery: Nov 2015)
Bongo Drums are fun with the Makey Makey. More software links from Makey Makey are available!
Here's a collection of Scratch games that work well with the Makey Makey.
Students enjoy using Play-Doh to create game controllers with paper clips, sharpies, and paper! Of course you can also make your own playdough!
Extend the possibilities of a Makey Makey with the Little Bits Makey Makey Module!