An article directory is one of the many places to place your articles. This method allows people who are interested in your product or service to see your article, view you as an expert in the subject, and (if you created your article right) – should visit your website.
The main directory to submit to is: Ezine Articles at EzineArticles.com
followed by Go Articles at GoArticles.com
These 2 are one of the best one’s to submit articles to.
Update: Post-Panda – Google it does seem have downgraded Article Directory sites and seem to favor sites that provide more value to site visitors. Given this – it would be best to check out related quality sites to link to your sites. This does take more time but in the end this is most likely what will last. Go for long term than short term gains.