I don't like very much new music, however once in a while something will get to me. As far as political or protest songs go, in 1999, there was Testify by Rage Against the Machine, and in 2004, there is American Idiot by Green Day, and Mosh by Eminem.
On the eve of the most important election of our lifetime, Eminem's video sums it up perfectly.
Here it is: Eminem's Mosh
Lyrics can be found here
(The best protest songs are still the oldies. Ohio by CSN&Y will always be my favorite.)