Yikes - this thread seems to have gone one forever! I just tried a few at random from several posts. And didn't seem to find any of what I would call "free". The most obvious ones being those that insisted on a payment, but most of those that didn't ask for money asked for a reciprocal link.
I think someone ought to point out that reciprocal linking is generally pointless. First up, you'll be putting a link to the directory on one of your pages, maybe quite a valuable page or even the homepage. The link they are going to give you is on some database driven page, full of other links, and buried deep within their site and more often than not (and with good reason!) the page your link goes on not only doesn't have any value, it's not even in Google's index! Even in a best case scenario you might get a link from a page that's as "valuable" as the page you add the reciprocal link on your site to. As far as Google is concerned if page A is worth 5 points and points to page B, and page B is also worth 5 points and points to page A the two links cancel each other out. Because they're worth the same. As stated above, the opposite is more likely - you are pushing the value of the page you are linking to.
The
PR of a given directory is generally meaningless as well - it's whether or not the directory in question actually gets any traffic (excluding traffic from people here looking for places to get free links). The only way to tell if that's likely to be happening is by checking the directory's SERPs
The is a directory of directories that are truly free at
Info Vilesilencer: The Original SEO Friendly Free Directory List.
I use that when I want to add a few free links. They carefully vet the sites they list, so you shouldn't get caught out with directories that add "nofollow" or javascript redirects to their outbound links to "hoard pagerank". I hardly ever do this anymore though. If you've spent an hour submitting your site to a bunch of free directories, you could have done far better to spend that hour crafting a polite and compelling e-mail to a webmaster of a quality site in your niche for a link. One decent link is worth a huge number of directory links.