You might want to try http://www.uniquearticlewizard.com/contact.html#downloads for a plugin for different types of sites including the two popular article directories.

You will get articles from the Unique Article Wizard system. Don't go too niche with this. Use upper level categories. Check out their uberarticles.com site for what the articles look like and categories are.

I am trying to build such a system using blogs in folders and subdomains, if my wpmanagerdx would just start working right. (not its fault-fault of hosting)