Monika Brodka became recently something like Florence + the Machine:
youtube.com/watch?v=-ycOABMpIyE
And this is the only nice tune I heard for recent months. Unfortunately those times are not anymore good times for Polish pop musicians. 90s were the times of good quality pop music, then came the crap, now there is almost non-existence of Polish popular music (I mean there is no a true star).
Gaba Kulka would be (literally) Polish Kate Bush.
For hip-hop: avant-grate rappers would be Fisz and L.U.C alongside with Polish downtempo producent Noon.
As for 50 cent counterpart... maybe Tede (but he makes a lot of gangsta mocking).
The cult Polish hip-hop musicians were: Kaliber 44 (not existing anymore), Paktofonika (not existing anymore), WWO (I don't know what's with them), Ostr, Slums Attack/Peja
There is a great fashion in Poland for reggae-like music.
I know Poles listen to more than just American music, right?
Yes we also listen a lot of British music ;)