I have had problems with my neighbors during my entire adult life. But, not with eye sores like your neighbor. I guess some people either just do not have pride in their home, whether they own or rent. And because they do not have the same view as you do, "out of sight out of mind", I suppose.
Our town just passed a blight law which specifies that grass must be cut (to avoid rodents hiding and Lyme Disease tick breeding grounds) and no standing water for two days (West Nile Mosquito breeding grounds), along with no junk or car parts or unregistered cars on the property for more than 30 days.
So, my suggestion is for you and perhaps other neighbors or other townspeople who live next to messy neighbors, you all get together and petition the town to enact blight laws. Sometimes the ONLY way to get people to be good citizens is to create laws to keep them in order.
Since our town passed the blight law, many properties have been cleaned up.
In a perfect world, all you would have to do is go over to your neighbor and kindly let them know that your view of their yard debris is not pleasant and they would say 'sorry' and remove the offending items. But, noooo, everyone has rights and can do what they want in their own yard. Right? Wrong....not with blight laws in force.