MRI online course: http://www.imaios.com/en/e-Courses/e-MRI
This online course has great animations to explain concepts and brief explanations. I think some of the animations are very helpful to explain details to students. You have to create an account to see the animations properly, but this requires little effort.
Virtual MRI (VMRI): http://www.iftm.de/elearning/vmri/idx_vmri.htm
This program can be easily run in your computer and gives a good idea about parameters for several sequences (Spin-Echo, Gradient-Echo, Inversion Recovery, Fast Spin-Echo), such as TR, TE, TI and ETL. Furthermore, it shows the k-space of the images and allows us to manipulate it and see the effect. Other image quality parameters can also be changed: FOV, pixel size, ... I strongly recommend this for computer classes where students have to apply their knowledge.
OSIRIX DICOM database: http://www.osirix-viewer.com/datasets/
This database contains several MRI datasets acquired for different regions (with and without pathology) and with different sequences. I usually don't use OSIRIX, because I don't have MacOS... I use one of the free visualization programs I referred in this post.