When looking for a quality web directory to submit to there are several key factors to look for.
1. What is the Pagerank of the page that my link will be placed on.
2. How many outgoing links are on the page that my link will be placed on.
3. What is the Pagestrength of the web directory.
4. How well is the web directory promoted.
5. Is the donation price permanent or yearly.
6. Does the web directory have AdSense or other advertisements.
7. If there are sponsor links are they site wide.
8. How well is the directory indexed.
If you find a directory that offers a permanent link on a page with a Pagerank of 3 or higher for 20.00 - 30.00 dollars I would consider this a good deal.
That may seem a little step to some but in reality your link is permanent and this is very cheap when you consider the alternatives.
You want to make sure that the outgoing links on a page are reasonable. I would say anything under 31 links is good.
Pagestrength is another tool to use that shows how well linked and the over all strength of the directory. Any directory that has a Pagestrength of 5 or higher should be considered strong.
Many directories do not have much traffic.
Look at the web directory and see if there is anything that would make you want to come back and visit it.
If so then this probably means others will be coming back also. Which is a good sign that the directory owner is putting effort into creating unique quality content other than just directory listings.
Another good sign and the obvious one that a directory is well promoted is if you see banner and or links on other websites pointing to that directory.
Many directories are now setting their review or donation fee to yearly.
In some cases this is good so the weak listings are weeded out eventually. In other cases it just just means it is going to cost you more in the long run.
If you see AdSense or site wide links being sold on the directory this is a BAD sign.
AdSense is a bad sign because this means when people visit the directory they could click on and leave the website through AdSense instead of your website.
Site wide links being sold is a sign of a weak directory. They are bleeding Pagerank out badly by selling site wide links.
This means less Pagerank is being passed to your directory submission.
You can use the site:www.webistehere.com command in Google to determine how well a directory is indexed.
You want to see how many supplemental pages there are verse normal indexed pages.
Generally speaking we like to see at least 80% of the directory indexed without supplemental pages.
For instance this directory only has about 1% - %2 of it's pages in supplemental results at any given time.
The less pages that are supplemental is a sign of the strength of the directory or any website in general.
These are just a few factors that will help you determine if a particular web directory is worthy of submitting to.
Directory Strength TestAgriculture Alternative Science Astronomy Biology Chemistry Earth Sciences Environment Mathematicst Science in Society Social Sciences SpaceTechnology