What do you guys use? I'm pretty happy with these for regular posts:
iSnare - $2 per article, sent out to ~50 000 article directories after review, which takes one week. Simple staple of article publishing.
Article Marketer - Free article submissions, tougher review regulations than iSnare and smaller distributions
With the odd item on:
eZineArticles
ArticleSphere
Of course all these are good feeds for human written content, too; ArticleMarketer and iSnare will HTTP POST to your site in a format you can easily decipher and do what you want with. Lovely for fleshing out that thing listings affiliate site
The last two provide content syndication via RSS. Most of these sites will give meta info such as keywords, title and category as well as the body text, which you can use to sort out articles that you want automatically. Have a go!
What I'm getting at, though, is - have I missed any diamonds out there? What do you guys use?