The more I use article marketing, the more I keep looking for new, good directories. This is because it's important to get those bio-box backlinks from many different places on the web. That does seem to help SEO.
Knowing that it is effective, I also want the new directories to approve my articles pretty soon. There's nothing worse than having submitted something and then not seeing it appear on the site for several days or even a couple of weeks!
But they still have to read your stuff, of course. If they don't, and just let absolutely everything that's submitted go up straightaway (and stay there) then the overall quality of the directory will suffer, and its rankings will drop.
That said, there are some article directories that are auto-approval, and still give you a good strong backlink. Go Articles is probably the best known of these. It's huge and has a PR of 4.
Then there's Article Slash. I've only just joined this one, but it's a solid directory with a PR of 4 as well. And your article goes live immediately.
I've also just found another PR 4 directory called Ezine Mark. Your article doesn't go live immediately, but I've only submitted one and that was approved within a day.
Another directory that published my article wihin 24 hours was ABC Article Directory. That has a PR of 3.
Articles Base is another huge, highly ranked one (PR 6) that is quick to approve (although it is nofollow).
Sooper Articles has a PR of 5. I quite like this directory and it's growing in reputation from what I can tell. I've submitted a few articles there now and sometimes they get published within a few hours. Then other times it will take a week. I suspect they just get inundated sometimes and get a little behind.
The biggest and best of all (and with a PR of 6) is Ezine Articles. It isn't known as a fast approval directory. It's really slow while you submit your first 10, then it speeds up a lot. The time after that varies, but it's usually around a couple of days from my experience.
UPDATE: I recently submitted an article to Amazines, which has a PR of 3 now I think. That was approved in a few hours. That's a pretty solid directory that's been around for ages. The article URLs don't have the full titles in them, though. Maybe this has ramifications for SEO? I'm not sure.
I used Article Blast this morning. That now has a PR of 5. The article I submitted went live instantly, and it was indexed by Google within a few hours, maybe sooner. I know this because when I Googled for the title a few hours ago it came up.