Donated once to the EFF and the ACLU at different times. The incredible volume of spam mail, junk mail, and phone calls that I received from these two organizations convinced me to never contribute to them again, as well as likely costing them more than my donation.
My advice: Donate to a local organization, not a national or international one. They are less likely to have hordes of administrative flunkies to bother you later (and consume donation money), and you'll be helping the community you live in. There are good causes in every community in America.