Shuttle Endeavor at the California Science Center.
The Space Shuttle is amazing (and enormous)! We took the kids on a surprise field trip today down to the California Science Center in Los Angeles. If you have a chance, go see it. It's free to get into the Center, and it's $2 per person to see the Shuttle exhibit. Tickets are best purchased online before you go to make sure you can get in. They have a timeline of the entire Shuttle program which is awesome.
There's a lot more to see there too. What a great resource.