The Huffington Post published another great article about Belize, and while they seriously underplay Cayo, Xunantunich and Caracol are mentioned as their favorites. Blancaneaux gets a good mention too.
"Sure it has the beach, mountains AND tropical rainforest sprinkled through the country, but Belize also has its fair share of incredible archaeological wonders. Get an up close and personal look at Mayan ruins by traveling to any number of ancient sites-- our favorites are Xunantunich and Caracol."