In case your neighbors need any convincing:

Snags for Wildlife, from the Connecticut Department of Environmental Protection.
Snags: One species' eyesore is another's habitat from the Rappahannock League for Environmental Protection.
Save a Snag for Wildlife from Texas Parks and Wildlife.
Woodpeckers and Snag Dynamics from the Wildlife Conservation Society.
Critter Condos: Managing Dead Wood for Wildlife from the Wisconsin Dept of Natural Resources (in pdf format).