According to Atwood's law this was a predictable happening. These are the ones that I know about but I'll be keeping this list up-to-date in the future:
- https://www.circuitlab.com/editor/ by NerdKits, L.L.C. utilizing jQuery, jQuery UI, jqPlot, jQuery Mousewheel Module, Raphael, Raphael SVG Import, Eve, OpenJS Keyboard Shortcuts Module, bootstrap-dropdown.js
- http://upverter.com/eda/ by Upverter Inc. utilizing jQuery and probably GWT.
- http://www.digikey.com/schemeit by DigiKey utilizing jQuery, jQuery UI, jQuery UI Widget, jQuery UI Mouse.
- http://www.circuits.io/ (added on 2012-10-14)
Although the above webapps are schematic drawing tools I can foresee fully-fledged online EDA solutions getting implemented in the future.