Leeside is a great place - I second that.
Email Bobby at Caye Accomodations - she manages a nice mix of places - from small private homes to luxury beach front rooms.
http://www.cayeaccommodations.com/Amanda does the same thing - but mainly focuses on private homes:
http://www.cayecaulkerrentals.com/Also check out Kim & Susan at Barefoot Beach:
http://www.barefootbeachbelize.com/Michael & Luciana at Oasi
http://www.holidaybelize.com/Two other nice places near the split:
Mara's
http://www.toucantrail.com/Maras-Place.htmlCosta Maya
http://www.toucantrail.com/Costa-Maya-Beach-Cabanas.html