Linking is basic; you get as many people as possible to link to you, and you link to whoever you want to link to. You can never have enough one way links. The more directories that link to you, the better it is for you. Most SEO consultants submit to hundreds of directories, and there are free resources that can help you (in a semi automated fashion) submit to thousands of websites. Any software that guarantees full automation is probably lying, since most directories now use graphical images (captcha) to verify whether the entries are being made by humans.
Most submission software offer great lists (all free). I use www.submithelper.com however there is some very good software that gets great reviews over at the Seochat forums. It is called submiteaze and it ranks number one for "directory submission software." Here is the discussion thread. Submit helper ranks number two for the same keyword phrase. Both applications work great but submit helper is free. It is similar to Roboform in that it auto completes specific fields in forms.
Submit helper also has lists of niche directories and paid directories. If your budget covers it, submit to every single directory that will have you (including any niche directory in your specialty). Niche directories are especially good at bringing in targeted traffic. This is good because it ensures that only traffic which has been searching for your site via going through the directories will get there. Some good directories for sites that sell online medications include www.rxlist.com and www.drugs.com. These are the biggest directories for this niches; there are dozens of others.
You should always keep it in mind that you are submitting to directories in order to increase your back link count. Note that search engines consider links from directories to be very good, since the links have been vetted by the human editors on the directory. A great list for some of the other top directories can be fond here at Blue Pearl.
Note that you don't have to use the software to help you submit links to hundreds of sites, but it is far more convenient than just searching for directories and adding your URL to them. However some of the directories listed on the software listings (especially Submithelper) are somewhat obscure, so here a list of top directories that should juice up your PR when you get them to link to you.
When it comes to links, I will take volume over quality any day. Get all the free links you can, then start paying for paid directories from highest to lowest cost. You always have to look at it from a cost benefit basis, and a lot depends on the size of your budget. A few hundred directories charge less than $15 a year, while several others charge almost $300. However you look at it, it pays to "go with the free."
Directory submission
Submitting your URL to directories is the beginning of your linking program. It is the easiest way to start and an assured way of getting non-reciprocal one way links. After this you can start actively link trading (which is like dating). Hopefully you would have a backbone of several hundred backlinks and an appreciable PR before you start reciprocal linking.
Web Directories 
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