One of the best upcoming Polish artists at the moment has to be Monika Evans
She sings, plays piano and writes her own music
I bought her new album called Nomen Nescio, but you can listen online at her website: monikaevans.com (8 songs in English and 3 in Polish)
Also one of my favourite Hoobastank covers by her too on Youtube 'The Reason'
Respect
Przemo