$BTC Here are some popular BTC coin pairs:
1. BTC/USDT (Bitcoin/Tether)
2. BTC/ETH (Bitcoin/Ethereum)
3. BTC/LTC (Bitcoin/Litecoin)
4. BTC/BCH (Bitcoin/Bitcoin Cash)
5. BTC/XRP (Bitcoin/XRP)
These pairs are widely traded on various cryptocurrency exchanges. Let me know if you'd like more information on a specific pair!