Looking in particular for SQL and RStudio courses, but would be interesting to know where the best materials overall are these days, free or otherwise.<p>I was pretty underwhelmed by Coursera's Duke SQL course.
For SQL, CodeAcademy is good. <a href="https://www.codecademy.com/catalog/language/sql" rel="nofollow">https://www.codecademy.com/catalog/language/sql</a><p>For R, <a href="http://tryr.codeschool.com/" rel="nofollow">http://tryr.codeschool.com/</a><p>For RStudio, just download and explore. You'll learn the essentials of using it in no time.