For civil rights songs, consider Tom Paxton's "Goodman, Schwerner and Chaney", or some that Judy Collins recorded like "It Isn't Nice", "Carry It On" and "In the Heat of the Summer". Related to the civil rights movement but not exactly a protest song was Janis Ian's "Society's Child." And did someone already mention Paul Simon's "He Was My Brother"?

In my opinion, one powerful anti-war song was recorded once and not heard of again. Joe Frazier of the (Chad) Mitchell Trio did it, called "Business Goes On As Usual." It deserved a wider audience.

For general, all-purpose protest purposes, Bob Dylan"s "The Times They Are A-Changin'" covers a lot of topics, including the civil rights struggle (the reference to standing in the doorway).