I wonder how Dmoz was able to get their directory marketed. But anyway, what are the best known ways to market directories.
Two techniques that seem quite effective when done properly: Blogging: http://www.avivadirectory.com/downloadblog/ Running an affiliate program: http://botw.org/helpcenter/resellers.aspx
There are many ways that you can promote a directory, traffic on the net is rising and it is easier to find new people this days, for example I have seen a lot of people promoting their site in social websites, others simply use pay per click search engines to drive traffic to their site, word of mouth etc, there is really no excuse for a webmaster to say that he can not get traffic to his website.
Is it a general directory, or is geared towards a specific niche? If it is geared towards a specific niche, then I would find blogs in that niche and leave useful comments on them to get started. Start a PPC campaign, even if it is only $20/day for a week. Start a blog yourself for the site, it is fairly easy to drive traffic to a blog, especially if your directory is built around a niche. Target that niche and hit it hard.