I can recommend Foundation Beyond Belief, at https://foundationbeyondbelief... . It is a humanist organization, so they are explicitly trying to just do good without promoting a religion.
They forward your money on to other causes (and it is clearly identified what they take as overhead, and you can reduce/increase that as you wish). They vet those causes for effectiveness. Every quarter they change who they donate money to, and you can adjust where your money goes within those groups.
They have an easy system to setup monthly payments, as well as giving you your end of year tax form, so it's painless to spread out your donation over time.