There are plenty of webmasters out there who are looking for people to write search engine optimised content. I have one regular seo writing gig and the odd request for keyword rich articles. One of the problems when you write for this market is that a lot of clients want their articles stuffed with keywords and this is not best practice when it comes to seo
Keyword Density
If you are trying to especially Google, then stuffing an article with keywords is not the answer. A lot of articles contain 2percent keyword density so if you are writing a five hundred word article that keyword whould be mentioned ten times. My regular gig is less than half that and they do a lot of business - so articles that have the main keyword at the beginning of the article,
once in the middle of the article, and again right at the end. Secondary keywords go in about 5 times. Many seo writers also use the long tail, which involves splitting a keyword phrase, finding synonyms for a keyword phrase and then mentioning them a couple of times throughout the article.
The above tactics make the writing more search engine friendly, more in line with how search engines read text, and more likely to get higher traffic as people often use different search terms for the same service or product. It's a good idea to practise these things in your own work as writing seo content
can get you a higher rate than other types of writing.
The_Walrus
Pro 
It is, of course, rather annoying to serious ethnomusicologists (to take a random example, that is perhaps not unconnected with myself) that articles we write for the benefit of other ethnomusicologists are pushed down in search listings by these hacks who are just churning out stuff to distort the search engine results. It does make serious research much harder, but of course, the hacks claim they have a right to write drivel for money, even if it results in humanity as a whole being less able to make good use of search engines. Best wishes!
Rebetiko. Walrus. Doctor Dark. Bouzouki.