Google Cardboard, being assembled by someone wearing Google Glass (Source)
Unlike the expensive and high quality Rift and Vive headsets, and the even more expensive computers required to run them, Google Cardboard takes a modest, low-tech approach to VR that's accessibly to everyone with a modern smartphone. A cheap and simple headset, initially made from cardboard, you slot your phone into the front and this becomes your display. Google's Cardboard app, and many others that are Cardboard compatible, are available for both Android and iOS, and compatible headsets are available from dozens of manufacturers for all budgets.
Anatomyou VR - An exploration of human anatomy in VR. Available for Android and iOS.
Bosch VR - Some of the artworks of Hieronymus Bosch converted to an immersive 3D experience. Available for Android and iOS.
ThinkLink 360 Degree and VR for Education - Information about a pending tool from ThingLink that will allow you to mark-up 360 degree images the same way you can for 2D images on ThingLink.
VR Lessons by ThingLink - A proof of concept from ThingLink demonstrating the capabilities of their new tool. Allows you to explore distant and exotic landscapes augmented with context specific information. iOS only at the moment.
Daydream Review - First impressions with Google's Daydream headset, the updated and more sophisticated replacement for Cardboard.
Daydream Review 2 - A second, more positive review of Google's Daydream VR headset.