Blender is a powerful, professional, and free open source 3D graphics tool that can be used to produce everything from single 2D stills, to full 3D movies in broadcast and cinema quality, and even interactive 3D content for stand-alone playback.
The program comes packed with essential features. A comprehensive modeller supports a range of 3D object types, and fast skeleton creation and automatic skinning help you get started; an in-built raytracer complete with halo, lens flares and fog effects delivers top quality rendering; animation tools support full armature deformation with forward/ inverse kinematics, adding automated walkcycles along paths for easy movement planning; and you get top quality diffuse and specular shaders, accurate physics and particle modelling, even collision detection to aid with real-time 3D game creation.
Once you've finished, your project can be exported for viewing as 2D images, videos (AVI or MOV, say), or a host of 3D formats for possible reworking elsewhere: 3D Studio, AC3D, DXF, DirectX, Lightwave, MD2, Motion Capture, TrueSpace, VRML, and more.
Note that this is the portable version of Blender.