Mark Niemann-Ross explains how you can donate to the R Foundation:
I benefit from the work of the R Foundation. They oversee the language, but also encourage a healthy ecosystem. CRAN happens because of them. Updates to R happen because of them. useR! happens because of them. Every day, you and I are the recipients of some part of their time.
The least we can do is show them some appreciation. If you point your web browser at https://www.r-project.org/foundation/donations.html you’ll find a convenient (and surprisingly inexpensive) place to express your appreciation. As an individual, you can send these kind folks twenty-five euros to tell them you’re in favor of what they do.
But be sure to read the whole thing, especially if you are an American who wants the donation to be tax-deductible. I believe that earmarking in this case is adding special instructions on SIAA’s PayPal page.