Try the Exotic Caye Beach Resort @ www.belizeisfun.com.
About a 10 minute walk into town, nice beach area, great beach bar called Crazy Canucks, above ground pool. You can also email Kat @ firstname.lastname@example.org. She has a one bedroom condo at the resort that she rents out and she gives an awesome price.
Depending on what you want out of your vacation, I would agree with Rulrich. If you want seclusion, stay north of the cut. If you want more excitement, stay south.
Email me @ email@example.com if you want to know more about the Exotic Caye. I stayed there in May. Will be staying there again in September and already booking my stays in 2005.