The human body is a cool piece of equipment and it's wonderful when we're blessed with one which works well. As a die-hard DIY'er I've always been fascinated by the signals that the body and brain generate in the course of our daily existence. Electrical signals are produced by the brain along with others generated by our muscles, the heart for example. Modern electrical components have made it possible for the hobbiest to construct his own equipment to tap into these signals and record them as digital information or translate them into sounds or graphics. Biofeedback and stress monitoring instruments can be home built at relativly low cost and even a modest computer can process EEG signals and use them to control game objects and cursors. You've probably read articles on this site describing the IBVA, a commercially available device for recording and utilizing brain signals. Here at the studio we use this along with DIY gear to tap into the electrical world of people, plants, and minerals. There are a few things to be aware of before you run out and grab the neighbor's skater kid for your experiments. It is not difficult to incinerate a volunteer when making the marriage of the body and electricity. Volunteers are hard enough to find without carbonizing them with ill designed electrical equipment and they may have family members who will dislike you for days and days thereafter. Be absolutely sure of what you are doing and read everything you can get your hands on concerning the body and electricity. If in doubt, DON'T! I 've been shocked by radio transmitting and receiving gear and it really, really, sucks. That said, here are a couple of sites to check out on this very subject. Enjoy.
This one has some open source stuff for EEG construction projects. I'm not sure how often it is updated though.
Catholic University of America offers this site with biomedical engineering projects.