Submitting to hundreds of directories is extremely risky. This tactic can cause your website to be penalized. I advise submitting only to a few authority directories.
A directory that is gaining popularity is scribd.
You can check its page rank. I think it is now PR 7
Scribd basically allows you to upload a document or pdf file. The site's number of readers is just impressive.
Aside from scribd, I also consider ezinearticles, articlebase, goarticles and articlesnatch great choices.