I have tried both the eoddata and HQuotes (Yahoo supplied by CSI) services and both are terrible quality for anything other than casual testing of a trading strategy.
Problems include missing or incorrect dividends, missing corporate actions (such as spinoffs - sometimes even splits).
For futures data, the free data sources regularly have bad ticks, do not match the exchange's data - some even have the wrong tick size (i.e. impossible values).
If you're trading futures/commodities you have enough capital to afford a decent quality data feed.