The OpenBCI project is an open source project with the goal of expanding the availability of hardware for maker experimentation with brain wave measurement. It was recently fully funded on Kickstarter. According to the developers,
OpenBCI is a versatile and affordable 8-channel EEG signal capture platform built around Texas Instrument’s ADS1299 Analog Front End IC. We designed it to give you access to high-quality, raw EEG data with minimal power consumption. OpenBCI is compatible with any type of electrode (active or passive) and can interface nearly all modern electronics prototyping platforms such as Arduino. OpenBCI is supported by an ever-growing, open-source software framework of signal processing and data analysis algorithms.
More information, including links to the schematic and source code can be found at the OpenBCI project page.