The American Academy of Neurology (AAN) has a site where you can donate to help fund brain research. All overhead for the donations are covered by AAN so all of your donated money will go directly to fund research into neurologic disorders. If you or a loved one suffer from a brain disorder or disease, this is a great way to potentially help others with neurologic disorders.
The minimum donation is $5.
Note: I am not affiliated with AAN or the donation site; I just think it is a great cause.