Across the U.S., Discover found the highest tippers are in Wyoming, Idaho, and Nebraska, while the worst were in Arkansas, Nevada, and Montana. Generally, those who lived in New England as well as East South Central region (Tennessee, Kentucky, Mississippi, and Alabama) tipped the highest—about 17% on average.
Link
Also, the chart on how much people tip different types of service-providers is interesting. Apparently I don't always tip people I should.