For Tuning:

Ninja Tuner - An awesome online tuner!

For reference pitches:

Violin A string     Violin D string     Violin G string     Violin E string

Viola A string      Viola D string      Viola G string      Viola C string

Cello A string      Cello D string      Cello G string      Cello C string

Bass A string      Bass D string       Bass G string       Bass E string

Metronome - to help you work on keeping a steady beat.

Flash Cards - to help you with note reading.

Music Theory Exercises - to help you with a note reading, rhythms, key signatures, scales.

More Music Theory Exercises - a variety of music exercises to practice.

About your Instrument:

Violin      Viola      Cello      Bass

Staff Paper - you can print off blank staff paper to compose your own music.

Finale Notepad - music writing software to ompose your masterpiece.

Sheet Music - free sheet music (with some recordings) for your instrument.

J.W. Pepper - where I purchase orchestra music; do a key word search for the piece you want to see/hear.

Interactive Guide to 100 Musical Instruments – Check this out - Fun!

Musical Glossary! - A nice Music Glossary of common terms. Thanks to Anna for sharing!