Verticals directories have been around for some time and can be a very good way to promote and list your web site or business. I found a good article a while back  by Julie Mason,  Practical Guide to Vertical Search Advertising at Search Engine Journal.

Julie provides a nice summary what verticals are why you should use them.
-More leads, less money
-More visibility
-More options
-More support
-More targeted

Many of these reasons are things that I have mentioned at various times before regarding local search. From what I have seen, many small local business are taking advantage of verticals, probably because they do not know they exist.

How do you find vertical directories to use? Go to Google or your favorite search engine and type in “vertical directories” or “lawyer directories” or whatever your field is. This should provide you will a nice list to review. Localsearchguide.org has a list a verticals on their web site.

Finally, Sebastien Provencher at Praized Blog, late last year provided his Local & Social Media Predictions for 2007, where he had vertical directories listed one of the key areas for local search. “Verticalization: The success of generalist social networks and online video sites in 2006 means that we will see the arrival of a multitude of new specialized players in these two fields.”

What he is saying is that vertical (specialized) directories are going to increase and is an avenue that local business can use to promote and build their on-line visibility.  So if you have not thought of using vertical directories, spend some time investigating what is out there. Odds are you will find a directory or search engines related to your field that you can get listed in.