Suppose I have 4-7 people in different cities around the US. They need to meet, doesn't matter where as long as there is a reasonable hotel with a conference room. Is there a website or method to determine the best central city to meet in? A city which minimizes the overall agony (cost + time + layovers) of all participants at once.
If for some reason you can't do an online meeting or conference call, I have three tips for planning a business meeting (not a conference or a vacation, where flight convenience is not the controlling factor).
Know your group
When dealing with business travel, it's important to remember that the ticket price is not the only cost incurred; time is also significant, especially in case of irregular operations. If you're choosing between two airports, pick one that is a hub for whichever airline the most members of your group have frequent flyer elite status with. The elite status means less time waiting in line and priority service if something goes wrong, especially if one has a lounge membership. Ultra-discount airlines, on the other hand, are right out.
Assuming your group is more concerned about time and convenience than about cost, I would argue the most important thing to avoid for an important business meeting is a connection.
Nonstops do command a premium, but that's because they're often worth it for business travel. So I would aim for a city which has nonstop service from the airports where the various group members will be flying out of. Depending on the particular distribution of your group, this is most likely to be a relatively hub of one of the Big 3 (United, Delta, American), but it could just as easily be a focus city for Southwest, which offers frequent nonstops from medium-sized cities.
Most major airlines have an interactive route maps on their website, which will help you visualize service to and from a particular airport.
On the ground, most things will balance out. Every major airport will have some business class hotel nearby with adequate meeting facilities, mediocre food, and a free shuttle from the terminal. The cost will vary depending on the location, but the cost of the room rental will probably be far below the cost of the flights anyway.
But schedule well, both time of year and time of day. San Francisco sees many fog delays in the summer, while Miami gets overwhelmed during winter holidays. Philadelphia gets delays for no good reason all the time. Flight delays cascade throughout the system and compound through the day: when an incoming flight is delayed, it is often delayed in departing again. The first flight of the day, having had all night to arrive and undergo maintenance, is far less likely to see a delay. So don't schedule a dinner meeting in Chicago in August and expect to have everyone there on the dot.