There are many peer reviewed studies showing the benefits.
Two good brands that i have observed success using together with therapeautic success are:
Now - http://www.puritan.com/mood-support-066/dopa-mucuna-velvet-bean-extract400-mg-072121
Himalaya - http://www.himalayahealthcare.com/herbfinder/h_mucuna.htm
According to some studies, the herbal product is sufficient at a dose delivering 1/3 the L-dopa content of the parmaceutical dose of Sinemet. Sinemet causes damage via pro-oxidant activity to the substantia nigra over time. The mucuna seems to work via another mechanism since the herbal lacks carbidopa. The therapeautic effects take longer to manifest, but last longer, the 'off-on' syndrome in Parkinsons is diminished with mucuna vs. Sinemet, in my observations.