Just a word of caution.
If you want to do ESTIM, PLEASE read up on it FIRST.
Don't attempt StereoStim or electrostim with homemade items as incidences have occurred where you can COOK your penis from the inside out.
From what I have read, and hopefully soon can try out... Electrostim is wild.
BUT...you have to make SURE that it's SAFE and done properly.
Theres a Yahoo Group dedicated to it, and many other Forums as well that give advice.
I downloaded a program called SmartStim, which you can play a tone that was generated by experienced users. Attached is a snapshot of it.
Your Headphone Jack connects to an amplifier box, and then from the amp to electrodes to your genetals.
Do Not EVER NEVER EVER NEVER EVER put electrodes on your Nipples or above your waist.
Doing so would cause a heart failure, or irregular heart beat that could KILL YOU.
Here's a link to give you a visual on the retail versions of the boxes.
You can make your own, and its pretty darned simple for a lot less...but again...you have to make SURE its correct..otherwise you'll be cutting off your wee wee. Electrical Units for Sale
Most popular, and cheapest are the TENS units, commonly used to treat arthritis or back pain.