And I shoulda thunka--

Suzanne Vega
Tracy Chapman
Keb' Mo
Richie Havens
Indigo Girls
Stephan Smith
Tish Hinojosa
John Trudell
will.i.am

There are thousands of people singing topical and protest songs from across the political spectrum, though. Attend the RNC or DNC, and you will hear quite a few more never discussed here, who now make up the bulk of political/topical singer-songwriters in the US.