Resources
Music Theory and Ear Training
http://melodycats.com/rhythm-cat/ (My favorite app for learning rhythms and note names! Download to your iOS device.)
http://www.musictechteacher.com/music_quizzes/music_quizzes.htm (music games, puzzles, and quizzes)
http://cornerstoneconfessions.com/2012/08/the-ultimate-list-of-online-music.html (ultimate list of online music games)
https://www.8notes.com/theory/ (for intermediate and advanced students)
http://teoria.com (for intermediate and advanced students)
http://www.dolmetsch.com/theoryintro.htm (for intermediate and advanced students)
Instruments, Sheet Music, and Accessories
Flute World: http://www.fluteworld.com (shipping is a little pricey, but super-fast)
Carolyn Nussbaum: http://www.flute4u.com
Flute Center of New York: https://www.flutes4sale.com/ (I have an instructor code which gives us perks such as free shipping and extended warranties and instrument purchases, so reach out to me if you decide to buy anything from this company. They also have frequent sheet music sales.)
Sheet Music Plus: https://www.sheetmusicplus.com (inexpensive shipping, but it can take a LONG TIME to receive your items. I have a discount code for purchases here, so reach out to me if you decide to purchase something here)
Flutey things
Flute Talk magazine is a great resource full of fascinating and educational articles written by master teachers: http://theinstrumentalist.com/issues/FluteTalk/
Jennifer Cluff is a flute teacher and performer in Canada who blogs here: http://jennifercluff.blogspot.de
Doctor Flute on Youtube: https://www.youtube.com/channel/UCH0s9yFGaPZ4eUb6XqkuqoQ
Just Another Flutist on Youtube: https://www.youtube.com/channel/UCq2gHrRVv2Z6Saf5FScqCaA
Useful Articles
On improving musicianship: http://blog.musicteachershelper.com/10-ways-to-improve-your-musicianship-in-2010/
On cultivating good practice habits: http://musiclessonsresource.com/for-students-10-music-practice-tips
On overcoming anxiety and stage-fright: http://musiciansway.com/performance/