Here are a few web sites I have found useful.

This list is just a start.  Many offer free things, some offer a mix of free plus extras if you subscribe.

Sheet music:

http://www.8notes.com/piano/

http://www.gmajormusictheory.org/Freebies/freebies.html

http://makingmusicfun.net/htm/printit_piano_sheet_music_index.htm

Theory:

To practise aural work and theory topics

https://www.teoria.com/en/exercises/

To listen to music:

Classical:

https://open.spotify.com/playlist/37i9dQZF1DWWEJlAGA9gs0

http://www.classicsforkids.com/

General Information:

Piano Technicians Guild - includes information on how pianos work, how to care for your piano

http://www.ptg.org

A wealth of information and resources for teachers, parents, students - everyone

http://pianoeducation.org/

Supersonics Plus

Here is where you can listen to  the Supersonics Pieces you may be learning. Just click on the album the piece is from and mp3 tracks will be available:

http://supersonicsplus.com/