It is interesting to see the variety, but the data is sort of conaminated by industrial users, particulaly east coal companies... If we limit the list to common carriers, the list will have fewer gauges.
Doug's first list was an eye opener if only because of how many narrow gauge locomotives were purchased in the 1860's... we tend to think of narrow gauge starting with the D&RG in 1871.
You might also want to look at the list in Hilton's Narrow Gauge Railroads in America, which he limits to 3' gauge common carriers, but lists by builder/by year. He also has a table based on builder and wheel arraingment.
Randy Hees
Randy Hees