I agree with Katie that the camp at Chaa Creek is a fine place (though the garden suites at the Lodge just can't be beat).
I'd also highly recommend Ek 'Tun lodge, which is in that same area but a bit farther up the Macal River. Phyllis Dart there does a wonderful job. Just two cabanas on several hundred acres of lush jungle, and the natural mineral water swimming pool there gets my vote as the best swimming pool in all of Belize. You can swim alone (nobody around to care if you skinny dip) and listen to the howler monkeys on the river. There are incredible caves on the property, too.
The two main lodges in northern Belize, Chan Chich and Lamanai Outpost, also are wonderful.
Pook's Hill and duPlooy's are a little mindful of Banana Bank, not deluxe but comfortable. Jaguar Paw is a little more upscale, with a more expensive restaurant and 24-hour air conditioning.