The following links all redirect to external sites.
Rigs
One of the best places where you can find rigged 3D models for Blender is Blendswap. Blendswap offers a range of rigs, from basic to production-style. You can choose to use it for free or with a subscription. Click here to visit Blendswap.
AnimSchool, an accredited online animation school, offers a free rig. The rig is known as the 'Malcolm rig,' and it is an advanced production-style rig that you can use in your own videos. The rig only works with Autodesk Maya. Click here to download the free Malcolm rig.
Another online school, Animation Mentor, is currently offering two of its rigs for free: