Even if I wanted to rank these, I couldn’t, because they’re too different. So I’ve listed them in alphabetical order.

Chris Brogan

Social media expert Chris Brogan has a great blog (I recommend it), but also a great email newsletter that provides additional content beyond what’s on the blog. Worth signing up for if you’re interested in social media.

Duct Tape Marketing

There’s a blog, a book and more, including an email newsletter, that are all part of John Jantsch’s acclaimed Duct Tape Marketing. The focus here is on effective marketing for small businesses.

Edge Editions

This is one of the few on this list that’s not focused on marketing and public relations. But as a marketer, or writer, or really just as a person, it’s important not to get so wrapped up in your daily professional concerns that you forget the big picture. And Edge.org is devoted to the big picture.

HARO

If you’re in public relations, or you just want to offer your expertise to reporters when they might need it, or if you’re a reporter who needs experts from time to time, then check out Peter Shankman’s Help a Reporter Out. It’s three emails a day, so the volume is pretty high, but I think this has become a must-read for many people, like myself, doing public relations work.

Jason Calacanis

Calacanis created a stir when he stopped blogging and declared that blogging was over. But he’s still twittering and doing other things, and he’s launched an email newsletter. It comes irregularly, but it’s smart and insightful. Calacanis has started some companies and made a lot of money on the Internet, so he’s worth listening to. As a bonus, he almost always asks questions and seeks feedback, so there’s at least a little interactivity built into this newsletter. Note that he is asking people to use their real names now (I don’t know how, or if, he confirms these) when they sign up.

MarketingSherpa

MarketingSherpa has great content on a variety of topics, everything from email marketing to interviews. A paid subscription to all of the content is pricey, but there are free email newsletters that get you access to some content for free. And even the free stuff is valuable.

On the Media

I’m often too busy to actually listen to NPR’s weekly On The Media show, but there’s also a website an email newsletter that will alert you to what’s on the show. I tend to think of On The Media as smart reporting by mainstream media mostly on the mainstream media. But it gives you a pretty good look into the issues that big media and mainstream journalists are often preoccupied with.

ProBlogger

Darren Rowse is one of the real authorities on making money with a blog. His blog is great for tips and ideas about how to be a better blogger, but his weekly newsletter adds some additional content beyond what’s on the blog. If you blog and want to do it better, even if you don’t want to make money on it, it’s worth reading his blog and also getting the newsletter.

Psychotactics

This site bills itself as focusing on “Why Customers Buy (And Why They Don’t).” The free newsletter is interesting, and often has links to other useful (and free) information.

The Publicity Hound’s Tips of the Week

Joan Stewart’s newsletter is full of creative public relations and media relations tips, as well as links to training opportunities.

What email newsletters do you subscribe to that you find valuable? Leave a link in the comments.

• Mack Collier writes about Nintendo’s extraordinary blogger outreach effort. Go ahead and estimate the cost per impression there — it’s amazing.
• Chris Brogan lists 50 ways marketers can use social media. Jeremiah Owyang organizes those 50 ways by objective.
• David Mullen suggests five ways Twitter will make you smarter.
• David Griner suggests five ways customer service can be improved with social media. I’ve left a comment on that post.

Any other great posts out there about social media and marketing? Leave ‘em in the comments.