This page will be used as a community wiki to list all the sites that can be used to buy or get assets to be used in your Unity games (3D models, packs, audio, textures, etc).
I found this site: bunbun.com.au. It allows you to view 3D models online in 3D using Unity Web Player. I think it's nice that it has all the 3D models in .unitypackage too.
There are a good list and review of websites with free content available at http://learningcsharp.co.uk/free-game-content/ it also covers the copyright and protection so you can know which free texture content you can use for commercial development which i found quite helpful because some of the websites can have quite fishy and unclear copyright protection. Happy hunting :).
Super Game Asset provide professional quality game assets for your game creation, including game icons, isometric renderings and tiles, portraits and game maps.
Free and Paid * http://www.flatpyramid.com, the 3d models are optimized for games, mobile, and augmented reality and you can view these optimized models in 3D.
You can also get free 2d graphics including sprite sheets and backgrounds from http://www.gamedeveloperstudio.com It’s also maintained unlike other free graphics sites.
