There are compilations of digitization vendors online, each with its own focus. (None though as truly comprehensive as I dream about.) Here is information on a list maintained by the New York State Archives of "imaging services vendors to aid government agencies, local governments, and other entities searching for companies and individuals providing imaging services. This inventory lists organizations, their contact information, as well as a brief summary of services offered when the information was available. While every effort has been made to ensure accuracy and completeness, you are encouraged to contact vendors directly for verification. "
* * * * *
Thanks to Geof Huth at the State Archives for his reminder about this list.