[Birdland]

Used to be Peoria, Illinois was the go-to for consumer market research.

[thackney]

Columbus was known for being a test market when I lived there 25 years ago.

We had the first Taco Bell / KFC / Pizza Hut combination resturant back then.

[Vigilanteman]

There are a lot of cities which have been mentioned as test market towns. The main criteria seem to be:

1. Somewhere in the midwest (though occasionally as far east as Pittsburgh, PA
   
2. College towns with lots of young people
   
3. Some place far enough away from media attention that nobody else will hear about it if the test product flops.
   
4. Some ethnic diversity is nice, but really not all that necessary. If the product is targeted at some particular ethnic group, they will pick a place where that group is prevalent.

Given the above criteria, that leaves a very large number of places suitable for test markets.

Our own Pittsburgh area is actually a fairly good blend of southern redneck, polite midwestern and east coast snob culture. You can find great examples of all three within an hour's drive of our fair city. We have a black population fairly close to the national average and what we lack in Hispanics we more than make up in Indians.