http://www.electro-cap.com At a minimum, the cap should have electrodes over hand and feet areas (C3, C4, and Cz). Additional channels can be used for control (CP3, CP4, CPz) and for spatial filtering as well, which will improve the signal quality.
Wilson, J. A., Schalk, G., Walton, L. M., Williams, J. C. Using an EEG-Based Brain-Computer Interface for Virtual Cursor Movement with BCI2000. J. Vis. Exp. (29), e1319, doi:10.3791/1319 (2009).