| MC3 Cardiopulmonary | Michigan |
| MCA Computer Corporation | California |
| MCADCafé | California |
| McAfee, LLC | California |
| MCB Soft, Inc. | |
| McBreen Marketing | |
| McBryde Website Design | North Carolina |
| McCabe CM - Agent | Maryland |
| McCAD | California |
| McCann Systems | Connecticut |
| McCann Worldgroup | New York |
| McCauley Marketing Services | |
| MCCi | Florida |
| McColley Marketing Media | Arizona |
| McCormick Computer Resale | Minnesota |
| McCormick Systems, Inc. | Arizona |
| McCormick Systems, LLC | Arizona |
| McCreadie Group, Inc. | Michigan |
| McCrone Research Institute, Inc. | Illinois |
| MCD Electronics, Inc. | Colorado |
| McDaniel College | Maryland |
| McDaniels Interactive | Illinois |
| McDaniels Marketing | |
| McDonough Telephone Cooperative | Illinois |
| McDougall Interactive | Massachusetts |
| McDougall Interactive | |
| MCE Technologies | California |
| MCE123 | |
| McElroy Electronics Corporation | Massachusetts |
| McEnroe | Maryland |
| McFadyen Digital | Virginia |
| MCG Web Development, Inc. | Michigan |
| McGee Designs | Nebraska |
| McGilly Information Systems | California |
| McGovern Capital, LLC | New York |
| McGovern Consulting Group, LLC | Pennsylvania |
| McGrath Electronics, Inc. | Arizona |
| McGraw Hill | New York |
| McGregor Enterprises, Inc. | North Carolina |
| McGuff Pharmaceuticals, Inc. | California |
| McGuire Design | Texas |
| MCH Corporation | Tennessee |
| MCH Data | Missouri |
| McHenry County College | Illinois |
| McHenry County Computer Club | Illinois |
| McHenry Software, Inc. | North Carolina |
| McHenryCom Co., Inc. | Illinois |
| MCI, LC | Iowa |
| McIntosh Communications, Inc. | Nevada |
| McIntosh Marketing | |