Installers and alarm dealers typically partner with alarm monitoring companies. Typically medium-large alarm companies and maybe even large end-users operate their own monitoring stations, but a big portion of the market use independent /wholesale monitoring companies instead.
This edited list is partially taken from CSAA's "5-Diamond Certified" (an operator training program) directory, but is stripped down to only the wholesale monitors/independent monitoring companies on that list. There are many others not on this list and outside North America.
Here's the list so far. If you see a mistake or omission, just add a comment below:
North America
Acadian Monitoring Services
Elk Grove Village, IL
Acadian Monitoring Services
Layfayette, LA
ADS Security
Nashville, TN
Affiliated Monitoring
Union, NJ
Alarm Center, Inc.
Lacey, WA
Alarm Central LLC
Kansas City, MO
Alarm Detection Systems, Inc.
Aurora, IL
Alarm Monitoring Services
Monroe, LA
Alarm Tech Central Service, Inc.
Ronkonkoma, NY
Alarmco, Inc. – Boise
Boise, ID
AlarmWatch
Atwater, CA
All American Monitoring
Sarasota, FL
American Alarm and Communications, Inc.
Arlington, MA
API
US & Canada
AvantGuard Monitoring Centers
Ogden, UT
CMS Monitoring
Medford, NY
COPS Monitoring-Arizona
Scottsdale, AZ
COPS Monitoring-Florida
Boca Raton, FL
COPS Monitoring-New Jersey
Williamstown, NJ
COPS Monitoring-Tennessee
Nashville, TN
COPS Monitoring-Texas
Lewisville, TX
Dynamark Monitoring, Inc.
Hagerstown, MD
Fire Monitoring Technologies, Inc.
St. Catharines, ON, Canada
Global Monitoring Solutions
Denham Springs, LA
Grand Central Station
Hayward, CA
iWatch Communications, Inc.
Beaverton, OR
Loss Prevention Services, Inc.
Clemmons, NC
Merchants Alarm Systems
Wallington, NJ
Midwest Alarm
Sioux Falls, SD
Monitoring America Alarm Co-Op
Tulsa, OK
National Monitoring Center
Lake Forest, CA
National Monitoring Center
Irving, TX
Nationwide Central Station Monitoring Corp.
Freeport, NY
NEXgeneration Central
Providence, RI
Rapid Response
Corona, CA
Security Central, Inc
Centennial, CO
Security Partners LLC
Lancaster, PA
Security Partners LLC dba Response Center USA
San Antonio, TX
SecurTek Monitoring Solutions Inc.
Yorkton, SK, Canada
Sentry Watch, Inc.
Greensboro, NC
Statewide Central Station
Staten Island, NY
Superior Central Station, Inc.
McAllen, TX
Total Monitoring Service, Inc.
Sacramento, CA
United Central Control
San Antonio, TX
United Monitoring Services, Inc.
Columbus, GA
Universal Security Monitoring, LLC
Gainesville, FL