Here's an interesting look at P/E's -- Shiller P/E -- historical S&P price - etc.
Click across the top of this page to see various charts for their historical relevance.
You'll see the big blowoff top of 1999 -- the P/E was 44 !! That was the heyday of IPO mania and instant millionaire and back to the bread line... LOL The equivalent of the housing flipping market. Where EVERYONE you know was talking about buying houses -- back then -- the grocery store clerk told you about their day trading account...
http://www.multpl.com