Creative Commons Search
Search for images and audio with Creative Commons license. This great infographic explains CC licenses.
Some commercial products offer free trials or free student accounts. These usually come with limits on the use of the final product so be sure you are aware of those restrictions.
The GNU General Public License is the most widely used free software license. Look for this when searching for open source tools.
Search Engines & Lists
Free Software Foundation
Black Duck Open Hub guide to open source software
SourceForge collection of open source software including for audio/visual, games, graphics, etc
Resource Center from Ohio State's Office of Distance Education and eLearning's list of digital media specific tools
Individual Tools & Resources
(Unless noted, all are open source)
Audacity
audio editor
VirtualDub
video editor
Gimp
image editor/author
Blender
for 3D projects
Sketch Up
for 3D projects; not open source but educator and student versions are available
Autodesk
for CAD, 3D, and more. Not open source but free to students with some restrictions
Scribus
desktop publishing, layout, typesetting, and animated PDF
ImageMagick
for displaying, converting and editing bitmap images
Orgre3D
scene-oriented, real-time 3D rendering engine
Adobe Flex
application framework for building and maintaining expressive web applications
PureDyne
live audio/visual processing and streaming. Development discontinued in 2012
MIT's Scratch
to program interactive stories, games and animation; targeted at K-12 students
GitHub
free accounts allow hosting of open-source software products
Drupel
content management system for web design
Inkscape
vector graphics editor
GNU
Unix-like operating system
Joomla
content management system for web design
WordPress
content management system for web design
Snagit
screencasting tool; some limits on time length and storage