For collaborating with other educators I've used a lot of things:
*email (of course)
*Google Wave (before it died)
*Google+ (for another MOOC)
*Google Groups (for a Collaborative Learning Network, CLN?)
*Twitter (I follow interesting people, who post interesting things. Occasionally I post interesting things.)
*blogs (I post on Blogger, I read wherever other interesting people post)
As a student I've used:
*PBWorks (for sharing projects with other students)
*Google Wave, Google Docs (for working on collaborative projects)
*blogs (often Blogger, but some other ones where in there too, for collaborative work, sharing images, video, and of course text)
*Flickr (for sharing images for a project)
*a bunch of other things that I made an account for, used for awhile, then completely forgot about.
As an educator I've used:
*blogs (you can read all about that on the SoMe thread)
*D2L, Blackboard (LMSs. I use these for everything in every class. I don't even know how to keep a gradebook that isn't in an LMS. I post assignments, have students submit assignments, post readings/notes/demos/links/etc. Not sure I could teach without them.)
*yep, I'm pretty boring, because other than some software that's about it.
Results:
I love blogs, but find that students don't love them as much as I do. You can read all about that
here.
I probably couldn't live without an LMS or something similar. If I didn't have one, I'd probably build one out of a blog and/or wiki (or build one up from scratch, depending on how desperate I was). I find that some students take awhile to adjust to this approach (for example, I often get emails asking questions that are easily answered on the course site), and others really like it. I won't harp on this too much, because you all probably use them too.
Obviously I've used a lot of Google services, and some of these work better than others. The nice thing is that almost everyone has a Google account these days, so you're usually not asking people to create a new account. Google Docs works well for collaborative projects, and I've had students use this to good effect to track tasks/problems while working on group projects (I did not require the use of Google Docs, but did suggest it as an option). I'd love to see more of my students use Google Docs (or Google Drive now? I forget) for working on collaborative documents, but I don't force this.
I used PBWorks (then PBWiki) in a class I took, and it was definitely neat. The downsides are that editing pages requires some know-how, so it doesn't work as well for students who aren't tech-savvy. I use my LMS for most of what I'd use it for, so I haven't done much with it on the educator side.
I'm teaching some hybird/online courses next year, so I plan on adding video, podcasts, and interactive content (applets or HTML5 canvas most likely) in the future. These will probably be presented through my LMS, as long as I can figure out how.