Classic rap is one of the best things America has ever produced. Why shouldn't the Obama's have had the artists they like visit the White House? It's traditional for presidents to invite prominent artists to perform there. All this ignorant, and frankly racist, whining from commenters about rap is laughable. The cultural critique that inheres in classic rap music of the late 80's and 1990's is as relevant today as ever. Go to Europe (including eastern Europe) and hang out. Rap music, dj culture, reggae are all thriving and comprise the major cultural scene there. 
"I spread the message of hope and of unity. That's what gets me up in the morning. I can tell you what is wrong, but I can't tell you how to fix it. I'm a raptivist, not a politician. I deal in hope. " Chuck D
Thank God for rap music.