Finally, I spent some time researching Google Gadgets implementation
and implemented it successfully as MediaWiki widget: http://www.mediawikiwidgets.org/Google_Gadget
Previously I had some issues with it as there was no control over the
values in the URLs without escaping them, but Gadget wizard didn’t
really allow to easily copy unescaped values for the URL. To avoid
this problem, I added new feature to the Widgets extension to support
validation of parameters without escaping them so to use Google Gadgets widget, you’ll have to upgrade your installation to version 0.8.3: http://www.mediawiki.org/wiki/Extension:Widgets#Download_instructions
This dramatically expands the amount of widgets/gadgets you can install on your wiki – previously there were only Widgetbox widgets getting which required much more hassle and relied on the user account to be created on Widgetbox site which in my view reduced adoption.
So go to Google Gadgets catalog and grab what you like: http://www.google.com/ig/directory?synd=open
As always, help is available at http://groups.google.com/group/mediawiki-widgets or just post your comments here.