After getting our tickets the previous day, a friend and I headed out early to visit the volunteer-run Biloxi Lighthouse -- the one on all the license plates. The first cast-iron lighthouse on the Gulf Coast, it's been an icon of the area for a very long time.
Located in the center of Highway 90 (between east and westbound lanes), the lighthouse is easily accessed and open usually between 9-945 in the morning. It's a massive iron cylinder, so it heats up very quickly in the summer and no one stays up there long.
The view is great, the premises clean and the staff very friendly. They were actually military volunteers with their family, just telling guests about the lighthouse history and local area. It was a very nice experience with a great view.
My friend proved a bit afraid of heights, as the stairwell inside is supported primarily by a single steel pole running up the center of the lighthouse, which seemed worse on the way down as the walls expanded but the railing remained narrow. Claustrophobic people also struggle inside the tight space, especially near the top. While it's not actually that high (~40 feet?) it can seem like more on your way down.
I really enjoyed the experience and the history. I highly recommend it if you like both!