ESRI is the maker of ArcGIS and they have some great (and sometimes free!) resources on their virtual campus. I just finished working through one of their courses. They provided me with a certificate.
Besides just learning the software, this module had a lot of interesting information about projections, datum, and coordinate systems.
One of the coolest things we learned was that changing the project had massive impacts on how we view the earth (from 3D to 2D). This was a great interactive module we used for learning about the differences between ____ projection and ____ projection which include _______. Check it out here.
http://mbostock.github.io/d3/talk/20111018/azimuthal.html
Here are two more links that explain how the above tutorial was made. I am working on making one myself!
https://github.com/mbostock/d3/wiki/Geo-Projectionshttp://bl.ocks.org/mbostock/3711652
https://github.com/mbostock/d3/wiki/Geo-Projectionshttp://bl.ocks.org/mbostock/3711652