I am not going to debate Dave's
SEO knowledge - my only suggestion would be if you do this as a paid service, why don't you post your website, portfolio, and pricing online? If your knowledge is that good, maybe some others would be willing to pay for your services. I am not going to argue with you or anyone, I keep my posts on topic and add value.
As to this post I have had great success with EZINE, however there is a learning curve. EZINE tends to be one of the more particular article submissions sites, which is good it eliminates all of the garbage. EZINE also provides a huge amount of online training and education which can really get you to refine your skill level of article writing.
I will give you an example - if you Google "Obama Health Plan Sick" my article is mid way through the first page "Top 5 Reasons Obama's Health Plan Will Make You Sick".
This was picked up in 48 hours and has been up for many months. I received one client off of the article (that I am aware of), who thought the article was great - he purchased a
HSA, life insurance, and has given me around 4 solid referrals so far.
Not bad for about 30 minutes worth of work.