The 10 Year Treasury Note Yield hit a low of 2.09% on August 10, 2011, which is 5 basis points above the low made in December 2008 (2.04%) and 14 basis points above the 1941 low of 1.95% (Robert Shiller's data pre-1953). The yield closed at 2.28% today. Mutlpl.com has the historical chart going back to 1881. The site also has the S&P 500 P/E ratio, dividend yield, earnings, inflation rate and more. A 10Y yield below 2% would be interesting to see.
Historical chart of 10 Year Treasury Note Yield (source table at multpl.com)