There are so many of what I call "super" or "mega" directories out there. Somewhat like the online yellow pages, but often geared to a specific industry.
If you are having troubled getting your site ranked well (and you've done all the right things), you may want to consider looking at who shows up when you type in your specific keywords in a search engine.
The top 10 results may likely include some directory-type websites. It may be worthwhile to invest a few dollars (sometimes they are free!!) towards this form of advertising. I look at it like this: If you cannot get your site in the top 10, you should at least be listed in the directory of a website that is listed in the top 10!