This is the third in an ongoing series called “Beyond The Big Three,” which highlights social networking sites other than Facebook, Twitter and LinkedIn. There are tons of other social media outposts on the Web, and they’re great places for associations to curate content. The first two installments on Flickr and Delicious can be found here. Stay tuned.

What do you get when you cross Twitter with a traditional blog? One of two sites: Tumblr or Posterous.

Although there are some important differences, Tumblr and Posterous do have a lot in common. Both let you compile all types of media – text, links, photos, videos, audio clips and more – into a virtual scrapbook to share with your members.

First up, Tumblr.

(Don't mind my goofy thumbs up)

Tumblr users can “follow” each other, much like on Twitter. (Following doesn’t have to be reciprocal.) There’s also the option to “like” a post, or “reblog” it and add your own comments if you’d prefer.

As far as mobility goes, there are great BlackBerry and iPhone apps for Tumblr. Personally, I’ve found the BlackBerry one very easy to use. Tumblr allows for Twitter integration, so your posts on Tumblr can be automatically sent to your Twitter stream, and tweets can be sent to Tumblr.

Newsweek magazine has recently started using Tumblr. They posted a great explanation of “Why they Tumbl” on Tuesday. In the post, they fully admit they’re not sure how to monetize Tumblr, but that they hope it creates a dialogue between magazine and readers.

Next up, Posterous:

The great thing about Posterous is that it was designed to be used via e-mail. Simple e-mail anything you want – text, photos, audio, even iPhone videos – to post@posterous.com. Your subject line will become the title and the e-mail’s body will become the post itself. You can even add tags in the subject line by including a double parentheses: ((tag:socialmedia, photos, association)). You don’t have to set up an account before e-mailing — whatever your e-mail address is becomes the URL (http://youremail.posterous.com). (Although if you want a specific URl, I’d recommend signing up for an account first.)

Update Posterous via e-mail

Posterous is handy if you’re on-the-go and attached to your smartphone. Like Tumblr, the site also has a community aspect: users can subscribe to other users and marks posts as “favorites.”

Media Bistro has done an excellent job using Posterous as a community blog. People can submit contributions to a specific e-mail address, and three curators approve and post the content. Granted, Media Bistro isn’t an association, but it is an online community that uses Posterous as a user-generated blog.

The best part about the contributions? People who submit don’t have to have Posterous accounts – just an e-mail address from which to send content!

You can export content from Posterous to any other social sites on which your association has a following – and vice versa. Flickr, Twitter, Facebook, YouTube – you name it, you can automatically post information across the board with a simple e-mail.

So how can associations use these sites?

Imagine if conference and meeting attendees could easily submit their own videos and photos to one main aggregator. ASAE and The Center had a great online hub for ASAE09, and they also had a Flickr group to aggregate attendees’ photos. I think Posterous would have been a comparable alternative because it lets many people share different types of media in one place. Attendees (real-life and virtual) could contribute their own videos, photos and thoughts to the community to create a great “scrapbook.”

Check out the FAQs for both Posterous and Tumblr, and I also love this Mashable post comparing and constrasting them. Each has its pros and cons (Tumblr allows for more theme customization, Posterous lets people submit contributions more easily), but maybe one of them is right for your association.

If you have any questions about either Posterous or Tumblr, feel free to e-mail me at shannon@memberclicks.com!

(Posterous screencaps via Mashable.)