www.slsc.org/
A wonderful place to take the family! They have great exhibits and it's free to get in! (You have to pay for Omnimax movies, special exhibits, etc) You can spend a lot of time there and not spend a dime. They do a great job and it would be a shame not to support them somehow (just spring $8 for parking!). Yes, you can park free on the Planetarium side, but if you do, consider seeing a movie to support their mission: they do wonderful things for the community. I recommend the Discovery Room for kids 6 and under, Lego Mindstorms for those 7 and over, and catching an Amazing Science Demonstration (there's a crazy guy who does a hilarious, yet educational electricity show!)