I live in central Massachusetts; and looking for plant and flowering tree and shrub suggestions that will work well in full sun as a border between neighbors.
Have you visited your local nursery or garden center? They are often the best source for suggestions specific to your locale, plus they have the plants there for you to see. Another great alternative is to visit any botanical gardens or arboretums near your area and see what you like.
Another option is to post this same request in your regional New England Gardening forum - suggestions from local gardeners will make much better sense than responses elicited from across the country :-)
When you repost on the New England Gardening forum, you might want to add a bit about your goals. Are you looking for some privacy? If so year-round or only in warm weather? Do you want to block certain views? Are you just looking for delineation between your property and your neighbors? Looking to keep out pets, kids, etc? Are you interested in a mix of plants? Is is largely ornamental value you are looking for? A photo of the area in question, viewed from the house and toward or including the house is helpful as well.
Here is a link that might be useful: New England Gardening Forum