Typically, if you want to get paid for with your writing, you're going to have to make your own services known and do whatever people want you to write about. There aren't that many services that act as effective mediums for advertising your service, or they often pay too little compared to what you could be earning because they know there are a ton of people that want to try and earn money writing and thus the labor is cheap. If you want a good idea of what kind of services are in demand then you can go and look at the services subsection of the forum and see who wants what, or who is offering what at least.