We've found great snorkeling from shore on all 3 of the main Bay Islands of Honduras: Utila, Roatán, and Guanaja. It's easier to access imo on Roatán which also offers more activity options for non divers than Utila. The snorkeling on the north shore of Guanaja is absolutely world class - a whole different league than the others in my experience.
Not much to see snorkeling (from what I've read and my own recent experience on Caulker) without a boat on either Ambergris Caye or Caye Caulker, but there are smaller islands further south with good to fabulous shore snorkeling and the atolls have great options (but are a bit harder to get to and tend to be more expensive). We spent a week on Glover's Atoll in August and were treated to real prizes like huge nurse sharks, juvenile spotted drums, and huge spotted eagle rays every time we went out.