We recently launched http://sketchfab.com, a free service to publish 3D models online without plugin, using WebGL and HTML5.
We are looking for someone to code a plugin exporter to publish models directly from Zbrush to Sketchfab, using our API. We already have exporters for other softwares: http://blog.sketchfab.com/tag/exporters
We wanted to let you know that we've updated the Zbrush exporter plugin up to 4R7 and it's compatible with both 32-bit and 64-bit versions on OS X and Windows! (At last!)
You can also now upload in draft mode, letting you tweak all your settings on Sketchfab before publishing your model.