$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!