I love reddit. I really love the sub-reddit r/dataisbeautiful. Various redditors contribute interesting graphs and charts from all over the interwebz.
I leave you to figure out how to use these data visualizations in class. If nothing else, they are highly interesting examples of a wide variety of different graphing techniques applicable to different sorts of data sets. In addition to interesting data visualizations, there are usually good discussions (yes, good discussion in the internet!) among redditors about what is pushing the presented findings.
Another facet of these posts are the sources of the data. There are many examples using archival data, like this chart that used social media to estimate sports franchise popularity,
Users also share interesting data from more traditional sources, like APA data on the rates of Masters/Doctorates awarded over time and user rating data generated by IMDB (here, look at the gender/age bias in ratings of the movie Fifty Shades of Grey).
Other statsy subreddits:
r/samplesize: Here, you can post your own online research projects in order to (hopefully!) up you sample size. You can also work on your own research participation karma by participating in research.
r/HITsWorthTurkingFor: Redditors share links for Amazon's mTurk tasks that are particularly profitable. There is all manner of work available here (not all of it research based), but as mTurk is increasingly popular with academic researchers, I'm adding it to this list. I think this may be a valuable discussion piece if you talk about mTurk in your research methods classes and want to discuss the variables that influence participation (and how this may effect your research) as well as whether or not mTurk is really a random sampling of humanity.
/r/statistics: A place for all of your statistics questions.
/r/dataisugly: The opposite of r/dataisbeautiful. Can be used to teach students how to create good graphs by showing them how not to create good graphs.