As a member of NAfME, you get access to numerous resources. On their website, you can find different sections for teachers, students, etc. One of the resources as a teacher you can access is the Online Professional Development for Music Educators by Music Educators. Through this, you can get over a 100 hours of professional development. This is great, especially if you don't have a lot of opportunities to do this through your school.
Carnegie Hall has a great resource for music educators who teach K-5th grade general music. They list the activities by grade, and even tell you what you can use each resource for (i.e. teaching rhythm, meter, singing, etc.).
This website is great, and I use it every day in my classroom! There are lessons, exercises, tools, and even apps you can download on different devices. You could use this in a general or instrumental setting, and at any grade level.
The NAMM foundation is another great organization for music educators. On their website, they offer different resources for educators through the Music Achievement Council. They also offer some videos with 'tips for success', which can help you advocate and support music programs, and the 'business side' of teaching music.
Teachers Pay Teachers (TPT), is a great resource for lesson plans, bulletin boards, and so much more! While most resources are free, some you do have to pay for.
This blog is written by Wendy Hart Higdon, a middle school band director who has wrote tons of articles on directing middle school bands, and has an awesome recruitment checklist on here!
This website is run by Katie Wardrobe, and she has great tips on how to integrate technology into teaching music. She even has a few freebies, like a free iPad course!
This blog is run by Angela Harman, who is an orchestra teacher in Utah. She has several great posts on starting beginner strings, recruitment, and even re-energizing rehearsals. She also has a book on shifting, which can be tricky to teach.
This website has a bunch of resources! They have free, downloadable files like beginning of the year checklists. They also post a lot of instrument specific articles, like proper techniques and how to teach them.