Not worth spending more than 1 day the capital. We found it, a bit characterless and prefered the smaller villiages and towns.
Unique Suggestions: Spend a few hours at Belize Zoo, a bit expensive, but look at it as contributing towards the animals upkeep. I think a ticket was B$15 for an adult. Kids will love it as there are lots of little educational tips and notes around the zoo.
Don't even think about staying in Belize City unless you ablsoluetly have to. It's a dump and there appears to be nothing to see. There is a place opposite the city from the airport that is near the Jaguar Park that is much nicer,but I can't seem to remember the name. Run by americans seemed real nice even though we only stopped to eat.
Belize City is the only major airport, so you have to fly into Belize City. I would not reccomend staying there any longer than necessary. The city has a high crime rate & there is really no reason to stay there.