The problem with essay writing websites is plagiarism or variants thereof. If you are writing this essay for a purpose (be it a paper for publication or payment) that's not a good option.
On the other hand, working with others to "get the juices started" is possible and practical.
What is the theme for this essay that you need to write? For what purpose will it be used? Who is the target audience? Is it to be serious or can it have some humor in it?
Also, considering free association writing - just start writing with a couple of ideas in mine and go from there.
Hope that helps! Feel free to contact me if you have any questions
Dr. Tony Mitchell