7. Wilmington, NC
Your stroll along the Riverwalk -- past the churches, gardens, museums, shops, etc. of Wilmington's Historic District, or through the 67-acre Airlie Gardens (complete with over 100,000 azaleas and camellias) -- won't be marred by the foul fumes of industry. This coastal city's air quality is due, at least in part, to reduced industry, which isn't so good if you're looking for a job there, but pretty great if the job you do have takes you there.