I’ve discovered an easy way to render DEMs in 3D online using GitHub. GitHub can host and render 3D models. You can upload a 3D model and view it via your GitHub account online. You can also embed the viewer into a webpage, like this:
You will need to get your DEMs into stl format. To do this, I exported my DEM into a point cloud x,y,z text file. I then loaded this into the freely available MeshLab, created a surface from the points and exported it to stl format. Detailed instructions can be found here on how to do this.
Here’s another one:
DISCLAIMER: I’ve found sometimes the models don’t load with slow internet connections. If it doesn’t work first time, try reloading.