Michigan.gov has a great photo gallery of the Mackinac Bridge celebrating it's 50 years of service. You can view them here. I must admit that the photos would be much better if they did not have a large and ugly watermark slashed across each photo. The photos are broken down into three galleries - Scenic, Events (like the bridge's dedication ceremony), and Construction.
The Traverse City Record Eagle has a slew of articles about the Mackinac Bridge in honor of the 50th anniversary of the bridge's completion. The big celebration for the Mackinac Bridge will take place July 27 & 28 in both St. Ignace and Mackinaw City.
Read Big Mac at 50 for links to other articles at the Traverse City Record Eagle.
P.S. Don't forget to check out the Mackinac Bridge page at Squidoo.