"EliteTrader - The EliteTrader forums contain significant discussions on all aspects of trading. There is an in-depth section on algorithmic trading. While the signal-to-noise ratio is roughly comparable to other internet forums, there are some fantastic threads discussing implementation of advanced trading algos, so make sure to hunt for them!"
https://www.quantstart.com/articles/Free-Quantitative-Finance-Resources#free-financial-data
https://www.quantstart.com/articles/Free-Quantitative-Finance-Resources#free-financial-data