Today, I stumbled upon a website which publishes textbooks, predominantly on CAD. While browsing through it, I figured out that they have a set of free Inventor assemblies, that can be downloaded. They can be found on this page on CADCIM. Scroll Down to section Inventor Files. A set of tutorials in pdf can also be found at the following URLs.
Apart from CADCIM, there are other places where you can download Inventor Assembly and Part files for free. Check out
I shall try to update this blog post whenever I find more resources about free Autodesk Inventor parts or assemblies.