Blockchain.com — Hash rate, difficulty, transaction count, active addresses. Updated every 30 minutes.
FRED (Federal Reserve) — Fed balance sheet, M2 money supply, Treasury yields, TGA balance, reverse repo. Updated same day as official releases.
Finnhub — ETF proxies for S&P 500 (SPY), Nasdaq (QQQ), Russell 2000 (IWM), volatility (VXX), dollar strength (UUP). Updates every 15 minutes during market hours.