@AMNH: The American Museum of Natural History has a great Twitter feed--it includes links to happenings at the museum and content that can be shared with students on a variety of topics.
@digitalteacher: Cheryl Davis is an Apple Distinguished Educator who tweets lots of great resources + lesson ideas for social studies teachers.
@MTMS_at_NCTM: Mathematics Teaching in the Middle School is a NCTM journal, focusing on teaching math to students in grades 5 through 9.
Bring diverse voices in: Follow and reach out to authors, thinkers, scientists, historians, companies, institutions, etc. Shows students a global perspective.
Send voices out: Shows students they have a place in the world and demonstrates their own value.