3D Libraries

As a 3D Artist, your value lies not only in your ability to create, but your 3D Library. What that means is the works that you have either collected or created over your lifetime doing this particular field of work. This includes, models, textures, color palettes, etc... The list is fairly extensive. Sometimes we all need a boost to our repertoire. Most times it's not worth it to create it from scratch. With numerous base models that already exist it's really hard to justify devoting time to create a proportionate human from scratch.

That's where free 3D Model Libraries come in. Some are fantastic others are so so.

Grabcad 
Perhaps one of the better options after registering you have both the option to share models and download models free of charge. Other than having to register for an account there's no real downside to this other than perhaps that this is largely related to CAD;so the type of material uploaded tends to be architectural, inanimate, or of the non-organic nature.

DAZ
DAZ is weird. I wanted to like DAZ when I first tried it but I really couldn't. It's got the tools to make it great buts its promise of "FREE" is really smoke and mirrors since there's a premium for textures and certain model packs. It also doesn't have the ability to alter any of its existing models and if I recall correctly the models are not compatible with anything other than their program. It's still got some great models and you can rig and pose models freely in their program which is a great benefit all its own.

Aversis

Conceptually the same idea as Grabcad but on a much smaller scale. It's library consists of 5 items right now. However, it does include other benefits such as V-ray program tutorials and lack of registration.

TF3DM

This site includes models of all types human ones also. Because, of that there is an 18+ rating on this website due to the ability to upload nude models. Sometimes it's necessary. All of the models are free to grab and it certainly is one to hold in the memory banks.

TurboSquid

This place needs more quality as the uploads are quite random and scattered. Most are free some are premium. I think it truly depends on the uploader here. The nice part about all this is that the site is very accessible to someone non-CAD attuned. 

CreativeCrash

Has a great library all organized into multiple respective categories. On the downside this site is pretty much all a premium. A good premium mind you but a premium nonetheless. If you need almost finished models then this is probably your best place to look if you've got some cash to spare. There's around 9 pages of Free models with around 500+ in commercial or premium models.