I've got several prototype devices for doing this. I'm having someone else sort through promising abstracts. If anyone has any experiments to try or any other questions let me know. I don't have the facilities to do proper studies of any sort, nor do I have an licensing or legal authority to conduct any studies. But I'll gladly answer things from a guy-in-his-basement perspective.
There's been a bit of discussion about TDCS here on LessWrong. If you don't know what TDCS is here's an article from Technology Review.
Here's a company (soon) selling a DIY kit to build your own.
Here's a video from Journal of Visualized Experiments on how to administer TDCS.
Thoughts?