Barchart

If you need historical market data to backtest your strategies, Barchart is highly recommended. Their Excel downloader makes it incredibly easy to pull the data directly into a spreadsheet without dealing with complicated APIs. The best part is that their free trial is fully featured and is more than enough to download all the historical data you need. You can simply grab the data, save it locally to your system, and use it to rigorously backtest your strategies offline. It's an invaluable tool for any serious trader building their own systems.