yeah i have had quite a lot of work done on my tattoos in warsaw...
There are a few that are very good but 90% of them are not just bad they are dangerous!
The main one which is the most expensive as well is Junior Ink on ul Marszalkowska, go here if you want new school style, lots of colours and bright inks.
A new one which has opened and run by a friend of mine is Poison Heart Studio you can check out some of the work here
Third would be a place in prague but i have forgotten the name of it now! Hope this helps.
Email me if you need any more information