This extension removes all Wikipedia site banners (featuring Jimmy Wales, editors, founders or otherwise) from all Wikimedia sites.
This extension hides the site banner on Wikipedia, and all the other Wikimedia sites (Wikimedia, Wiktionary, WikiQuote, WikiBooks, WikiSource, WikiNews, Wikiversity, WikiSpecies, MediaWiki, Wikimedia Commons, et c), on all site language versions.
When a site banner is removed, a little page action icon with a crossed-over Jimmy Wales shows up at the far right of the page's address field, which, if clicked, toggles the banner back on (or off), for the current page. Hover it to see how many banners you have been spared so far (in total, and on the current site alone).
This extension is licensed under the Creative Commons Attribution ShareAlike 3.0 Unported License, as is the picture of Jimbo featured in its icon and screen shots. Full source code and revision history is available on the Developer website below.