Exchanges: Trading X for Y. What are the X's?

[Lostpike]

So one thing I have noticed is most the exchanges rotate around three groups in their trades of X for Y
1. ETH or BTC for Y.

2. FIAT for Y

3. Exchange based coins for Y (Like Binance or Tether)


My question is what other coins have a large amount of coins they can trade X for Y? 

I know that Monero and LTC both have a small amount on some exchanges but are there any other key exchange coins or maybe upcoming ones?