About 15–20% of my total income. I prefer to give as directly as I can to the point of use, since as @syz pointed out, many of the “umbrella” organizations skim off a surprisingly high percentage of donations as “administrative costs”(executive salaries and perks comparable to major corporations). Battered womens shelter, public radio (in three different states), Planned Parenthood, various medical research organizations; several advocacy groups for issues relating to women, GLB, firearms owners, civil liberties, etc.
I also give direct, anonymous aid to neighbors that I know are in need; I have paid the electric bills of two neighbors directly to avoid it being cut off(with the electric co-op told that they are not to say who paid it), bags of groceries left on porches, etc. I’ve also donated lumber and other building supplies to Habitat for Humanity.
My autistic nature (Aspergers Syndrome) makes it impossible for me to donate my time in a conventional sense. I have donated my engineering skills several times to organizations when I could do so without direct social interaction.