I use Amex Premium Rental Car Protection. It costs $18 per rental.
Last summer, I damaged a rental in France. I filed with Amex online and they contacted the rental agency, got all the documentation, and paid the claim. (The claim by the rental firm appeared as a charge to an Amex card; APRCP initiated a dispute to delay the charge until they finished their determination). Essentially all I got were status notifications. I think it took about 4 months to complete.
On another occasion, Payless tried to charge me $6500 for damage to a car, that I had returned undamaged. Again, I sent it over to Amex and forgot about it. About 3 months later, Amex informed me that Payless had dropped the claim.
I highly recommend this service when renting a car (FYI, coverage not available in Italy. Buy Super Cover from the rental company).