I got married at SunDiver and enjoyed it very much. They have a very nice beach for weddings. We actually got married on the pier. Here are some pictures if you would like to see them.
http://community.webshots.com/user/turnbun

I hear the beach around Banyan Bay is in very bad shape and the seagrass emits a foul odor, so check into that before you decide to get married there. Nothing like a smelly beach to ruin a wedding!

Iraida at Belizeweddings.com does a very good job of planning weddings on AC. She arranged everything for us.