Recommendations for a Galveston trip?

So I'm spending this weekend in Galveston. Most of the trip is planned, but I have an opening Saturday afternoon. Are there any must-see attractions? I was looking at Moody Gardens, but it seems very expensive for what you get. It's much more expensive than the zoo or aquarium, but doesn't seem to have as many animals as either? Do you think it's worth it?

I like history a lot, are there any good historical tours? Especially interested in the Great Galveston Hurricane and the pirate history of the island.