If you ever have the opportunity, visit the Cosmosphere in Hutchinson, Kansas. They have the actual Apollo 13 Command Module on display.
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The Cosmosphere's got a more impressive collection (though that Saturn V makes up a lot of ground for Huntsville) and the presentation is much better.
There's an OK zoo (great, adjusting for where it is, really) nearby, worth a stop if you're there with kids anyway, but not much else I know of in the area. It's weird that there's such a good museum so far from everything, including from the most-traveled highway through-routes for the state.
I'd also been to the Cosmosphere as a kid (the SR-71 in the lobby is how I recognized that one when I returned, haha, don't see that every day) and have been about three more times over the last 15 years, as an adult, and it's still great.