hi
I have created a mega menu button plugin
U can try it in the multi store demo site at
http://demo.online-ex.com/
It's a widget which accept any nop method that return a partial view
or
you can create your own view.
for the example i have included a all categories menu
(check the right button on the header menu)
for localization i used the string resource which should be changed manually
the full project can be download from codeplex at the changeset
http://nopms25.codeplex.com/SourceControl/changeset/changes/5a91c9290bf9
It's a multi store version of NopCommerce however u can download it and copy the Mega Menu plugin only