1) Space and Rocket Center
2) Ava Maria Grotto (though thats a ways away)
3) Historic Downtown
4) If you are going to still be here in September, Big Spring Jam will be fun
There is lots to do here Xand, I just dont know what you are interested in, etc. Lots of parks and hiking trails, lots of civil war stuff if thats your thing. A museum or three, some sport team is playing pretty much every night. Atlanta, Birmingham and Nashville are only day trips away. Several spectacular caves if you are a spelunker, (in fact Huntsville is the home of the National Spelunkers Association).
-Tig