Hit up Lick's Beachside cafe for some fresh fish and a nice atmosphere. They have a nice balcony and limited seating downstairs. We were there during poor weather so not much was happening, but we hung out and got to know the proprietor (a Canadian ex-pat) and some locals. It was lots of fun, casual, and relaxed. And the food was good. If you chat with the owner you're sure to hear some interesting stories, and probably hear about the drama with his beachfront tables. (From what I see on FB, this is an ongoing saga. There were no tables on the beach when I was there.)
For a bit more splurge, Hidden Treasures is worth the trip. It's far from any hotels and not on the beach, but if you make a reservation they will provide free transport. (Either they send their driver, or if he's busy, they'll send a cab to you and pay him on arrival.) The food is delicious. You feel like you're hidden away in the middle of the jungle. I thought it was great. Both my friend and I got the mixed seafood grill, which was a lobster tail, shrimp, and fresh fish. But skip the mashed potatoes, which are instant, and opt for coconut rice instead, which is divine.
We also went to Wild Mango's. The location is great, and the food is pretty good. I liked the other two better. Caliente also has a nice location but the food was just OK. Everyone raves about the chicken drop, which we missed because we weren't there on a Thursday, but I can't say I see the draw of watching chickens poop on the floor?
If you want more info and aren't getting enough here, I suggest tripadvisor. Search for "Restaurants, San pedro Belize" and you'll see a lot more information than you'll get here. Make no mistake, you will get excellent fresh seafood on AC, and if you opt for that, your meals will be excellent. But if you're from a major city in the US, don't expect the "fine dining" places like Red Ginger to be what you're used to. They're OK, but I'd opt for non-hotel places with simple seafood. That said, poolside at the Phoenix I had an excellent lobster tail for lunch from the Red Ginger kitchen, but their dinner menu was trying to hard to be fine dining and didn't quite live up, IMO.