Among the richest portals of public domain content are:
· Archive.org (Internet Archive)
· NARA (National Archives and Records Administration)
Compfight / A Flickr Search Tool
Foter, PhotoPin, and Wylio (great for bloggers!)
Getty Image (embed images with symbol for noncommercial use)
Pixabay (public domain photos)
Picdrome (public domain photos)
TinEye (search by CC images by color)
EduPic Graphical Resource (free photos & graphics for education)
World Images Kiosk (global images for academic use)
Jamendo
Free Music Archive
Incompetech Royalty Free Music
Vimeo Music Store (some pay)
MobyGratis
FreeSound
Opsound
ccMixter
Free Sound Effects and Loops
ArtistServer.com
Free-Loops.com
AudioFarm
Opsound
Internet Archive’s Netlabels Collection
Soundclick
SpinXpress
Open Source Audio from the Internet Archive
Public Domain 4U (lots of blues)
Purple Planet Music (Royalty free music)
Find Sounds Search for sounds and sound effects
Partners in Rhyme
RoyaltyFreeMusic