I’ve used various mod’s of this trick for different CMS’s over the years, here’s the one for SharePoint 2010 (thanks itgroove  Sean!).

So you’ve applied a new master page or page layout, tinkered with something you didn’t think was going to break in the UI, and now you’re left with a mangled wreck of a site layout  or an error screen you can’t seem to backtrack out of.

A simple thing to try: type in your site root and type in any page out of the main /_layouts folder, so something like:/

http://mysite.com/_layouts/settings.aspx

With any luck you will be returned to the pristine joy of the out-of-the-box SharePoint Master Page main site settings.