When I say «a good directory», I think primarily that:
- category pages should be static;
- the sites listed should be linked with static URL;
- the category pages should have good PR and not so much links on page;
- shouldn’t have too much pages for one categories (when you submit your site you are on the first page, but after 3 months, your link will finish at the fifth page, that has no PR.
Example of static page (URL): www.mydir.com/bussines.htm
Example of dynamic page (URL): www.mydir.com?cat=12
A good directory will pass PR to your site. Here is a directory that I intend as a good one (excluding the fact that not all category pages have PR). All pages, and links are static, there are not too much links on page (maybe the fact that some pages are rather empty penalises PR of the same pages), and the pages with PR have decent 3 rank.
There are also directories that will list your site for free, without reciprocal link, and in this case doesn’t meter if the page is dynamic, with dynamic link, without PR; the link is free, so it’s your convenience to have it.
It’s not a good idea to submit to the pay directories, those that insert your link without reciprocal link, but you must pay for the service. This kind of listings are in contrast with Google policy, and Google penalises this links.