Some useful background pieces….
Economist article dealing with risk-on and risk-off trades, published in November 2010
Mood swings, The Economist, 1 Oct 2011
A speech (with useful charts) called “Risk Off” by BoE Executive Director, Andrew Haldane, 18 August 2011
For measuring the degree of stock market volatility, using options prices, have a look at the VIX index.