Article marketing is an effective way to increase your search engine traffic. Three of the best article directories are Ezine Articles, Article Dashboard and Go Articles, which all have a PR of 6. I've been using them consistently and they really do help.
Still, it's worth spreading your articles around, since the search engines do like variety. So I've found a few other ones with decent page rank. These are: Article Pool (PR5), Article Click (PR5), Easy Articles (PR4), U Publish (PR3), Article Rich (PR3), Article Buzz (PR3), 365 Articles (PR3) and Post Articles (PR3).