BBC Sound Effects (Available under the RemArc licence. For non-commercial, personal or research purposes or for formal education purposes while you are a student or member of staff at a school, college or university)
Freesound (Aims to create a huge collaborative database of audio snippets, samples, recordings, bleeps, ... released under Creative Commons licenses that allow their reuse. For more information on licensing and attribution see the help page.)
PacDVD (Royalty free sound effects and some music tracks for use in video, film, audio and multimedia productions only.
Must link back to the website or mention "Music by www.pacdv.com/sounds/" in your credits.)
Partners in Rhyme (Royalty free music loops in Wav format. Suitable for use in YouTube videos and student projects. Requires giving Partners In Rhyme a link on your website or blog, a credit in your Youtube video or an email saying "Thanks!".)
Sheet Music and Scores
IMSLP / Petrucci Music Library (Extensive user curated library of public domain music. NOTE: Some music may still be in copyright in Australia as this is a Canadian site with different copyright duration laws.)