You should also consider Liquid Surf & Sail in Fort Walton Beach. I rented a windsurfer and rig yesterday, and can personally vouch for the quality of equipment and service. I enjoyed high end equipment at a great price. They also offer kiteboarding rentals and instruction.
http://www.liquidsurfandsail.com
I've also heard good things about XL Kites as recommended above.
By the way, the bay side of Gulf Islands National Seashore on Okaloosa Island is fantastic. It has strong winds, flat water, and it's chest deep for those times when you need to get started again. For windsurfing or kite boarding it compares well with the Outer Banks of North Carolina.
Have a great trip!