So Double Game (aka Torino Violenta) is on it's way from NoShame on the 28th March but Italian cop movies (often know as "Poliziotteschi") are often overlooked with Giallo's and Horror all'Italiana getting all the attention.
However its well worth investigating this genre as you will recognise many of the actors from other Italian cult movies and best of all they are generally highly entertaining, violent and totally non-PC. The scores in these movies are of a real high standard as well with contributions from Ennio Morricone, Goblin (famous for scoring Suspiria and Profondo Rosso) and Francesco de Masi.
Its hard to know where to start if you are new to the genre, but Fernando di Leo is as good a place as any. In my opinion he has made some of the very best, with Milano Calibro 9 one of my favourites. Other well known directors of that era also made valuable contributions to the genre, inlcuding Umberto Lenzi with "Milano Odia" and "Milano Rovente", and Sergio Martino with "The Violent Professionals"
Another set of titles I urge to track down and enjoy are the Nico Giraldi movies, starring the excellent Tomas Milian. Often directed by Bruno Corbucci, they are part crime/part comedy which is a nice break from the more serious Di Leo titles. The only drawback is that very few have been released on Region 1, with more having seen the light of day in Italy without subtitles. The one I recommend to start with is Squadra Antiscippo (Cop in Blue Jean) as it comes with English subtitles. If you are proficient in Italian then head to Thrauma DVD and go nuts!
Italian Crime Films @Xploited
Raro Video of Italy have released many of Di Leo's classics onto DVD and they all generally come with English subtitles, so go check them out.
Scorebaby have loads of reviews of the groovy soundtrack you won't be able to get out your head, and then you can buy them at Moviegrooves.
PollanetSquad is an excellent resource with loads of info on the genre. In Italian only.