I know you may be wondering if it really possible to get unique contents for free, but I can assure you that it is very well possible and you can start getting unique free contents for your blogs as soon as you finish reading this post.
There are lots of content service website available on the internet, from which bloggers can get unique free content for their blogs, but it’s not "totally free", you will usually give a link or two as a credit to the author and I think that is a fair deal!

1. My Blog Guest

My Blog guest (MBG) is an awesome community of bloggers and guest bloggers who are willing to give you their unique contents in exchange for a link from your blog. It is own by Ann Smarty, a well-known blogger, and social media user.
I love My Blog Guest because this site has a lot of users and you will usually find an article that will suit your blog no matter your blog niche.

2. Post Runner

Post-Runner is a service that is very similar to myblogguest; in fact, most of the site am listing here are almost the same.
Post Runner lets you get guest posts from various authors in exchange for backlinks to their website of choice, and Post Runner just like MBG also has a WordPress plugin that makes accepting and managing of guest posts easy.

3. BloggerLinkUp

BloggerLinkUp is quite different from other content service website that I have listed, BloggerLinkUp will let you subscribe to their list and you will get an email each Monday, Wednesday, and Friday.
These emails will list bloggers looking for expert sources, requests for guest posts, bloggers and webmasters offering guest posts, and PR reps and others seeking reviews of products. When you see a request that you can fulfill, just respond directly to the requester.

4. Post Joint

Post Joint is another place to get free unique contents for your blog, Post Joint connects advertisers with blog owners. Advertisers produce quality content and bloggers offer to publish their guest posts.
Post Joint streamlines the prospecting process matches the audiences up and takes care of quality control. Simple as that! The best thing about post Joint is that you can earn some money too.