I have been on Pinterest for years, collecting both professional and personal pins. I have tons of recipes and craft ideas that I will never get to!
For my social studies classroom, I followed Social Studies Success. She creates solid lesson plans and resources for middle and high school.
For Library ideas, especially elementary library, I follow Mrs. Lodge's Library. She has great ideas for centers and interactives in the library. Of course, I also follow School Library Journal, a great periodical dedicated to library.
Innovations in Technology is a good place to find tech. integration resources.
For me, Pinterest is a great place for library bulletin board and decoration ideas and ideas for library skills and reading promotion.