NASA is an amazing resource for STEM education. They have multiple sites and programs, with multimedia and lesson resources for educators.
NASA also has a speakers bureau that will provide engineers, scientists, and other professionals to speak to audiences around the country. You can also request an astronaut to come and speak to your class. It is free, but there are some conditions. It is an easy process.
A new resource that is really exciting and fun is the STEM on Station resource. This is education's connection to the International Space Station and includes lesson plans, videos and news. There are opportunities to connect with the space station and research conducted there as well as other great resources.
This is a great resource for any teacher, not just STEM.
NASA - Find lots of great educational resources