Pete Seeger represents a bygone era of protest, but arguably his most famous song, a version of Guantanamera, was not a protest song but a love song about a girl from Guantanamo. Ironically it makes a perfect protest song today simply by changing the ‘a’ to an ‘o’ and only open source software pioneer, Richard Stallman seems to have seen this. The second clip included here shows Stallman singing it.
Guantanamera is possibly my favorite song – as my wife can testify after I downloaded 7 different versions and played them on rotation for a week.
There are some other classic versions below the Stallman one, by Celia Cruz and Joseito Fernández. Add any more you can find in the comments