Tidy rendered HTML output in Chrome's View Source?

I recommend Quick Source Viewer.
It can show you the source of the current page formatted and colour coded.

It's pretty powerful, showing all 'sources' of the page, be it css, js or html. Even things like inline css/js can be viewed individually (with injected code highlighted). And the best part is it prettifies all of them, even the css (which chrome's dev tools still refuses to do).