NASA is an excellent resource for educators with sites, lesson resources, and more available.
One of the resources I really like, and use each year, is the Rockets Educator Guide. NASA has recently updated it with some new information and materials. It's available as a free PDF download here.
The NASA - The Rockets Educator Guide includes lesson plans and activity ideas. This guide has some great activities like rockets using film canisters, baking soda, and vinegar, paper rockets, altitude trackers and more. There is even a part on the history of rockets.
I use this at the end of the year in a project on Rockets, combining topics from throughout the year in a fun project.
Here's more on the project: http://educationaltechnologyguy.blogspot.com/2011/05/rockets-great-project-for-end-of-year.html
More NASA Resources:
Quickly find free NASA educational resources
Here are a lot more great, free Educational Resources from NASA