COT data is one of most used tools for gauging forex market sentiment. We wrote about a lesson in our school,
http://www.babypips.com/school/getti...ith_forex.html
There's also a newsletter available by Market Vane,
Market Vane, but subscription is required.
You can also use the
Dollar Index (USDX) and look for divergences against the majors. For example, if EUR/USD (inverted), GBP/USD (inverted), USD/JPY or USD/CHF is rising and USDX isn't, it's a good early warning signal of a possible reversal.