This question has been already asked a couple of times.

Probably you can find something here:

http://www.italki.com/discussion/66777

http://www.italki.com/discussion/66065

http://www.italki.com/question/246092

Traum - Cro

I recommend you to search for Roger Cicero :) 

I think at the moment the most popular german artist is Cro. I like him very much. But there are a few artist here in Germany. But most of the time (in Charts) we listen to american music. Also in clubs we listen to David Guetta or so. For learning german I think "Fettes Brot" is quite hard, so I think Cro is much easier. Its still very fast but easier to understand. Sido is also quite easy

I recommend Xavier Naidoo, especially songs : "Bitte hör nicht auf zu träumen" und "Dieser Weg".

I also like this songs:  Sido- "Augen auf", Sido & Adel Tawil- "Der Himmel soll warten" , Christina Stürmer- "Ich lebe".