Mixamo
Mixamo is an innovative 3D character animation service that helps game developers and animators acheive desired animations better and faster. Features include characer re-targeting, auto-rigging, sequence editing and a library of thousands of animations. All animations can be downloaded in .fbx, .dae, or .bvh file formats.
Unity Asset Store
The Asset Store gives you benefits of scale the world's largest game developers can only dream of—right inside of the Unity Editor. While developing, you can easily leverage the work of professional content developers and other Unity users in your productions. When you're done with your game, add an extra stream of revenue by putting your work up for sale.
Turbosquid
TurboSquid is a digital media supply companythat sells custom-built and stock 3D models used in 3D graphics to a variety of industries, including computer games, architecture, and interactive training. As of 2011, TurboSquid had over 225,000 3D models in its library, making it the largest library of 3D models for sale in the world.
CGTextures
CGTextures is a texture website that supplies good-quality textures in an organized manner. The textures are all royalty free and can be downloaded with a free or paid membership.
Free 15mb/day $63.00 per year for 100mb/day $128.00 per year for 250mb/day$258.00 per year for 750mb/day
Official Site

Mayang
Mayang is a free texture website with over 4000 free to download, high-resolution textures.

Free Sound Project
The Freesound Project is a repository of Creative Commons licensed audio samples. Sounds uploaded to the website by its users cover a wide range of subjects, from field recordings to synthesized sound effects. All audio content in the repository is released under the Creative Commons Sampling Plus License, and can be tagged and browsed by folksonomic means.
Arroway-Textures
Arroway Textures is a manufacturer of high-res textures, which are used in many areas of digital visualization, e.g. architecture, design and art.
The 3D Studio
The3dStudio.com is a great 2D & 3D resource site on the Internet. They have a collection of 3D models, printable 3D models, stock photos / images, and textures for programs such as Autodesk 3ds max, Photoshop, Cinema 4D, Lightwave, Maya, Vue, Blender, and many others is vast and it is growing larger each day. You can also sell your 3D models, stock photos and images, textures, etc.
3DOcean
3DOcean is a royalty-free 3D models, textures, concepts, and materials and shaders.
AudioJungle
Buy and Download Royalty Free Music Loops and Sound Effects from our huge range of stock audio for use in web, broadcast, corporate, presentation and other uses!
Sound Dogs
Sound Dogs is an online commercial sound effects and production music library
Ranges from >$1 for sound effects to $100 (or more) for music tracks Educational Price: Up to 35% off

3DRT
A market place for 3d models.
Opuzz
A royalty free music collection.
CuePop
Production music for absolutely no charge. A database of high quality professional music of top composers.