"Add blog post"
"Send a guest post"
"Submit an article"
"write for us"
"Become an author"
"Guest bloggers wanted"
"contribute to our site"
"Submit a guest post"
"Submit Post"
"Submit blog post"
"Become a guest writer"
Those are some ideas to get your juices flowing, make sure you add the " " and then put your niche and see what comes up! i.e google "Submit a guest post" your nich keywords
If you were to do this everday, you would gain a significant boost in traffic.