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If you are willing to pay to get listed then Yahoo! should be top in your list.
Increase link popularity? If your site get listed in ODP, it means you will definitely get additional links from hundreds of ODP clones out there.
Getting listed in ODP might get additional rank of one in Google Page Rank. For example, if your site PR is currently 3, your ranking might go up to 4.
There are thousands of free directories out there. Unless you are willing to take the trouble to submit to "all" of them, you shouldn't waste your time if your PR is already 4 or 5, because a few links wouldn't be enough to increase your PR further as one or two links from sites with PR 3 or 4 is enough to get PR of 1 to 2. Additional links would easily increase your PR to 3.
I am speaking from my personal experiences.
--No pr on the page where your link is likely to appear
--302 or even 301 redirects on the links (which tells the search engine that your content is now theirs)
--the link page is in a frame (which search engines can't read)
--they have a "more info" or "details" page with YOUR title in their title (so they are a direct competitor for your keywords)
--100+ links on the page (Google will ignore anything over 100)
--Directories banned in their robots txt
--alphabetized links so the link changes pages often
--too many banners, logos, thumbnails so the page loads too slow for the bots
--dynamic URLs with too many paremeters in them that will produce no PR.
And a lot of these have the nerve to request a link trade before you submit too.