My favourite online model-viewer Sketchfab now supports animations!
While this is still in beta I expect it to be available to everybody soon. I joined the beta test and tested the animation feature using one of the animations I created for my wyvern game asset. Since the rig of this model makes use of a lot of fairly complex IK chains/switches/etc. but doesn’t utilize any shapekeys/morph targets (which aren’t supported yet) it seemed perfect. You can view the result right here in your browser:
To my delight I was awarded a Staffpick Award shortly after I published the model. :)