Looking at a 1 minute chart of ES or NQ, you will many times see volume spikes at the point where the market changes direction, at least briefly.
I've done some testing with TradeStation and have found that if you look for extreme volume spikes, and wait for a candlestick to confirm a new direction right after the spike, you can do a little better than 50% picking up a point or two.
I haven't actually traded it, because it's counter-trend trading (I prefer trading with the trend) and the probabilities aren't high enough for me to be comfortable with it. But I believe there is some correlation between volume and price direction in at least these 2 index futures.