Directories provide link that aren't in-content, therefore they have low value to the search engines' eyes., ESPECIALLY for Google which is the best to analyze wheiter a link is meaningful or not.
Do I need to remember you that PageRank is from Google?
You could submit your site to 1000s of directories (and to answer Simon's question, I doubt there is more PR8 than DMOZ and Yahoo) but you will see very little benefit from it. Okay, a $299 Yahoo listing can do some good on Yahoo search results, but you have to be ready to pay the price.
Some directories provide no-follow link (mostly free ones, look for that before wasting your time suscribing).