I had to dig through their site to find this, as it wasn't immediately noted on their donation page, but they are a 501(c)(3) non-profit and donations should be tax-deductible for US taxpayers.
FYI: it's on the front page, on the top-right container, labeled "Welcome to the Archive". But the site isn't the best layout on the internet, it's pretty easy to miss.
Wow. Haven't felt so blind in a while! Good catch.
I doubt you're alone in that :) And it's quite possible your comment here will be seen by more people, so it serves its purpose :D
And some employers will match charity donations, so you may be able to double your contribution!