[spacemanaki]

I discovered the "verbatim" option under the "More search tools" link on the left hand side recently.

http://support.google.com/websearch/bin/answer.py?hl=en&...

It's not as convenient as an extension or a script, of course.

[sp332]

It should be easy enough to write an extension or even a bookmarklet for this. You just have to add &tbs=li:1 to the end of the URL to enable "verbatim" mode.