There are 63 lighthouses (and range lights) in Prince Edward Island, giving it the largest concentration of lighthouses in North America. Many are still in operation. I visited PEI twice (in 2010 and 2011) and visited lighthouses both times.
North Cape Lighthouse
Lighthouse at Fort Amherst
West Point Lighthouse
West Point Lighthouse
Cape Bear Lighthouse
PEI offers a "Lighthouse Lovers Certificate" through its tourism promotions, where you collect stamps or fulfill requirements at various lighthouses, like East Point and West Point. I got the certificate on my second visit (with Mom and Dad).
Victoria Seaport Lighthouse Museum
Souris Historic Lighthouse