SEO, or search engine optimization, is the art of making web pages attractive to search engines; and SEO writing is the art of turning out content with the right wording to catch the search engines' eyes. What this means, mainly, is tons of short articles with carefully calibrated keyword densities.

The quality of the average SEO article is... Well, speaking as an SEO writer with a profession to uphold and my dignity to defend, the average SEO article is poo. Content-light, padding-heavy, with bizarre twists of diction to make the keyword phrases fit into the text, frequently written by someone who's willing to work for a quarter-cent a word and for a webmaster who may not speak enough English to realize that what he's buying isn't, strictly speaking, English. There's a vast range of SEO writers, from the people working for fractions of a penny per word in Southeast Asian sweatshops to the people making $250 for a 400-word article.

If you're looking for work to do at home that won't drain you too much for schoolwork or more intellectual writing and that pays at least as well as a job at the local supermarket or office, the two-cent to five-cent plateau is the place to aim. The articles are short--300 to 500 words--and undemanding, so you can turn out one or two an hour at an average rate of $8 to $20 an hour. Finding good jobs isn't too hard if you know where to look, and the competition isn't fierce. The level of writing skill required is on the level of a competent high-school or college essay--which is why the competition isn't fierce. You won't get bylines or the chance to express yourself, but you will get paid regularly.

If you want to aim higher, you'll need about the same level of writing skill, but the articles will be more complex and you'll need to do more schmoozing to find jobs. This is the level of the professional freelancer, not the part-timer. If you're aiming for this level, skip to the page on freelance web writing.

Freelance Writing: Morning Coffee
A daily roundup of freelancing gigs. The jobs are mostly better-paying and more respectable than SEO writing, but SEO work occasionally appears on the list.

Freelance Writing Jobs
Freelance writing gigs aggregated from across the web. An excellent place to start, with hundreds of SEO writing jobs.

Flexjobs: Telecommuting Online Content Jobs
"Online content involves the written and graphic content that appears on website domains and other forms of online advertising, entertainment and corporate sites. Skills needed for working in online content can include writing, editing, marketing, graphic design, SEO, SEM, and social media."

DigitalPoint Forums
The lowest recesses of the dank and slimy pits of Hell. There are two reasons to go here:

1. To look for the two or three remaining jobs that pay more than a cent a word.
2. To feel better about your own prospects as an SEO writer.

Your best bet for finding jobs is to hang out at the Copywriting Forum, where the better writers go to chat. It's not explicitly for job-hunting, but because that's where the good writers are, that's where the better clients go. The cheap writers and stingy clients are in the Buy, Sell, or Trade: Content Forum and the Content Creation Forum, where the going rate has been sliding steadily downward from a cent a word since 2008. It used to be more amusing before they forced writers to stop replying to every. goddamned. post. that. came. along. ("hi i am great writer i can do this job for u pm me") Now it's just an endless litany of people buying and selling articles for ridiculously low prices. Not the worst place to get your start if you need a couple of published samples, but as a career plan, you can do better.

oDesk
A site for telecommuters of all types, from writing to web design to accounting and programming. Look in all sections of the Writing & Translation section, not just the obvious ones. [Note: oDesk requires workers to use software that lets clients see workers' progress during work hours. If you think this is intrusive, you're not alone.]

Craigslist - The Craigslist "writing/editing jobs" and "writing gigs" sections occasionally get requests for keyword article writers. Check as many cities as you have time for.

Elance has frequent calls for keyword article writers under Writing & Translation > Web Content, but I hesitate to send you there. Elance is an auction site (so it takes longer to be hired), and bidding on projects can cost money. It's a venue best left to established writers.

SEO firms often keep a stable of writers, whom they send a steady stream of work. Sometimes they advertise on job boards when they need new writers; sometimes you have to make the rounds, emailing them a cover letter and your writing samples.

Articles and Content
An SEO firm with its own stable of writers. They pay about a cent a word and have a board where you reserve topics and spoot out articles. Email them and ask whether they're taking on freelance writers.