This is the best cappuccino both of us has ever had. The service may have been slightly rude and we did have to pay I think probably 1 euro more to have it outside at a table but it was totally worth it.
As the name suggests it is on Piazza di Sant'Eustachio, just near Piazza Navona. You can buy the beans to takeaway too, which I wish I had done. But we did come away with some beans from Tazza d'or which also made a decent (not the best) coffee.