Directories play an important role in link building campaign.The weight of the link from a directory is still questionable but they do count as back links.Finding the right directories is as important as submitting your site to one.There are free and paid directory services.The paid services have better results as your website gets listed in no time and there is a guarantee that it will remain listed for a specified duration.On the other hand free directories do not offer quick service in listing your website and there is no guarantee at all that it will remain listed there.This factor should not be overlooked if your want to have long lasting links from web directories.
Many directories only offer one way links to your website i.e you do not need to link back to those directories by placing the link of those directories on your website.
I will not list down all the free directories here because you can have the the list of almost 100 such directories from Blogging Mix . There are all free directories with high page ranks and the good thing is that they do not require a reciprocal link so there are just one way links from high PR directories to give a boost to your site’s link popularity.