The Open Directory Project is the largest, most comprehensive human-edited directory of the Web. You can browse through the site at DMOZ.org. The sites listed here are replicated to the Google Directory, so getting listed is good for you.
DMOZ is constructed and maintained by a vast, global community of volunteer editors. Getting listed in the directory starts with selecting the search phrases you are targeting, and then finding a directory category that includes them. This task can be very time-consuming because there are lots of matching categories.
When you are submitting your site to the Open Directory, you should also think about second tier directories to submit you site. The Click and Search Directory is another good place to list your website.
Before you submit your site, you should find the most relevant category that does not have too many competitors in it. The editors will have the final decision as to what category your website will be located.
Related sites:
The Click and Search Directory: http://www.ClickandSearch.com/
The Open Directory Project: http://www.dmoz.org/