That's what I ask all the time while browsing. Then I select it with the mouse and click on the following bookmarklet:
It will pop-up a prompt which is already populated with the value of the selection, or you can copy and paste from another source.
Then it will simply alert the html code for you.
More about using bookmarklets: http://en.wikipedia.org/wiki/Bookmarklet
Fork the gist: https://gist.github.com/811331