Open Directory Project
DMOZ is the largest directory that is edited by people and not by search engine spiders, this has some benefits but also causes some problems.
As all the submissions are checked by people who are interested in or have expertise in the field that they are editors of the sites that get listed in DMOZ should be of the highest calibre.
However as some of the editors can be a little over zealous and will not allow sites that they do not approve of into the listings, also due to the fact that everything has to be checked by had a s it were the waiting list is growing ever longer.
The search engines are also giving the DMOZ listing less weight so it is becoming less desirable to have your site listed, although it is still worth going through the submission process, just be prepared to wait a while.