1. They generate real traffic by real people looking for what they offer, and are visited by more than just other webmasters submitting their sites.
2. They aren't just free-for-all listings where anyone can submit anything to any category, but instead are well-moderated, and all the links in the directory are useful.

That's the type of directory that will be around for the long haul, and you'll get the most benefit out of in the long term.

Keep looking for the site with high rank of visitors and they offer directory as well cuz these are the sites who will ppl look in it as cscgal said in nr.2

DMOZ is one of the most important directories according to what I hear.

there's a thousand list of directory submission sites that is very to use and no need of your reciprocal links..

check the PR of directory see if its SEO optimized and see how well its doing at google. Its takes real pain to get the real good list of same. I saw same listed at few places in this form i think search for this forum you will get that list.