These are some of the best resources that I have gathered for 3D models. You can say that there are two categories, modeling software and 3D model libraries. Let’s start with the libraries that I use the most.
Blender kit is a cool initiative that I learned about at the Blender conference at an early stage. It is an add-on for Blender that gives you access to their asset library right within Blender.
The add-on is even included in Blender and about half the library are free assets. I had to try it and thus paid for the premium alternative. The quality is generally higher than Blendswap but not excellent. The density of high quality models though is higher than on Blendswap and it is very well worth the low price. You can also upload your own models to Blendkit through the built-in add-on and make it available to people.
It is free and built in, so why not try it.
Blendswap is the traditional hub for free Blender assets. What makes me recommend it is that it is a good start. I also still use it when I need to put together a quick scene, for a draft or a feature image for an article on the website.
Be careful with the licensing though. The site uses a variety of creative commons license. For commercial projects, I would stick to those labeled cc0 if you find something of use here.
Chocofur store - By far the store that I have used the most. I only made one purchase since they have a bundle including almost everything in the store. They call it the Chocofur lifetime bundle and it is well worth the price. If you were to get the same amount of quality assets elsewhere the price would be much higher.
They focus on architecture visualization so if you are not in the field you may want to pass. But for anyone that is, this is a goldmine.
Chocofur also have a subset of their models released under cc0 license. If you are unsure if their models fit the bill for you, you can start to have a look at those.
How should I describe this? Take any 3D asset store and throw away all the things that you don't want and you get Flippednormals. The assets available on this site has such dense quality. There are few products that are not well-made here. Flippednormals curate the content to make sure that the quality is great. You don't scroll through page after page of low quality assets like you can on other marketplaces.
A huge collection of 3D assets. This site is enormous. This is also where I have chosen to keep my own models, it is very easy to upload and get going. An excellent platform all round. You can find almost any model here.
The list would not be complete without Blendermarket. But I almost never find myself turning to if for 3D models and assets. Blendermarket is more focused on add-ons for Blender and for that I use it a lot.
Graswald is a well-made pack of grass models that is easy to distribute with an included add-on for Blender 2.79 and 2.80. The assets can also be used in other 3D applications. The results are stunning, and for a reasonable price. I have used it in many scenes including these.
A well-made pack of rocks that you can throw into your scene whenever a rock is what you need. On the expensive side for rocks with plenty of competition these days. But these are the rock assets I find myself using.
The go-to solution for making 3D trees. A very fun add-on to work with. Pick a preset and grow the tree any number of years. Very intuitive and quick to get going. Then there is still a huge set of options available for any specific needs.