Well there's always the classics: Woody Guthrie, Pete Seeger, Utah Phillips, Joe Glazer, Anne Feeney, Joe Hill renditions, Paul Robeson, etc.
Punk music generally has a socialist undertone, but I especially love Rise Against. Some other good bands are Dead Kennedys, NoFX, and Anti-Flag. They're also actively anti fascist community; Nazi punks fuck off
My list is gonna be mostly punk music.
Fugazi, Minor Threat, Dead Kennedys, Dystopia, Discharge, G.I.S.M, Capitalist Casualties, Man is the Bastard, Aus Rotten, Nausea...dont wanna just keep listing punk bands...Mos Def, Talib Kweli, Black Star, Lauryn Hill, Dead Prez, Run the Jewels, KRS One, Bob Marley, lots of reggae...Zach de la Rocha + (Rage Against the Machine), Tom Morello (Nightwatchmen), Pink Floyd?, Woodie Guthrie...