I love Coursera! Here are a selection of courses I've taken, with a brief (personalised) outline:

Introduction to Data Science - This was the first course I took on Coursera, and it was a great eye opener into the world of free online courses. A great course which went from traditional databases to noSQL, to Hadoop on AWS, sentiment analysis and more, it really sparked my interest.

Social Network Analysis - This course provided a great introduction to some of the more interesting data mining you can do on graph data. From measuring influence with algorithms like betweeness and pagerank, to calculating the robustness of networks.

Machine Learning - A pivotal course by Andrew Ng, one of the founders of Coursera. This course has students building out a lot of machine learning models from first principles in MatLab to truly understand the mechanics behind them.

R Programming - I took this course to formalise my otherwise very 'organic' learning of R. A solid foundations course, it made me a lot more confident manipulating data in R.

Programming Android Application for Handheld Android Systems - Although I was comfortable in oo programming languages like Java, I struggled to find the time to learn the basics of app development. Quite simply, a few weeks on this course took me from unable to build apps, to being able to put together my first (drinking game) apps with relative ease.

It's also worth noting that while I really enjoy Coursera and the other sites like Cloudera, edX and Udacity, I really dislike the term MOOC, which sounds stupid.