I really suggest incorporating salescopy into SOME of your articles. HOWEVER, there are a few ways to do this and many ways not to. What I recommend doing is using a short little advertisement that is incorporated into what you are talking about in the article. For example, if you are talking about salescopy for autoresponder messages it would be easy to incorporate something about autoresponders into that article. Something like: An autoresponder service I use and recommend to you is (blah blah blah). Then simply continue on with your article.
I do this a lot in my newsletters. It is a way to get a little more traffic to those sites.
If you are writing articles for other companies I would put several short ads like the one mentioned about in it. Try to not make it sound like you are trying to sell them something but just mentioning it as a recommendation. This will help because if the article you write is very good you will be viewed as some sort of expert in that area and they will believe you if you say another product is worth their time to take a look at it.
Hopefully that helps. Send me a message if you have a question about what I said.