I have participated in paid post sites in the past which pay me, as the blogger, to write about a site or service.But there are many free guest posting sites from where you can get good quality dofollow backlink.Here is some sample sites

1.behance.net

2.livejournal.com

3.houzz.com

4.deviantart.com

5.medium.com

6.dailykos.com

7.hubpages.com