There are lots of options for printable flashcards on this link. Especially helpful for piano students are the "Grand Staff Flash Cards."
Educational Piano Resources
This site lists many aspects and links to the history of the piano, composer bios, and ideas for improving your skills.
African Music Circles
Here is information about musical team building workshops for drumming and world music.
This is a blog with interesting tid-bits about anything piano/music related. Look around and see what piques your interest - from learning about tuning and the insides of a piano to ideas for practicing and how to understand rhythms.
The Piano Explorer
Check out the Piano Explorer website online for FREE!
The San Fransisco Symphony has set up a website where you can find a music lab, different instruments in the orchestra, and play some music games. Check it out!
New York Philharmonic Kidzone
At the New York Philharmonic Kidzone you can find a game room, musicians' lounge, composers' gallery, instrument laboratory, a composition workshop, and much more!
Free Piano Music!
At G Major Music Theory you can download music for free at your level! They also have helpful theory pages and ways to improve your listening skills, which in turn helps you improvise and learn songs you hear but might not have music for.
Free Flute Music!
Flutetunes.com offers free downloadable flute music. It also includes theory info and much more.
Music Notation Software
At Noteflight you can set up a free account and begin writing your own music!
Learning about the Instrument
At Piano Technician's Guild website you can find activities for students - coloring pages, games, and interesting facts about the piano itself.