Coinbase and Kucoin are two popular exchanges. Kucoin requires no verification or ID and is based in Hong Kong. It's an exchange similar to Binance and it has it's own token.
Coinbase also has a $10 sign up bonus for new users that buy $100 of cryptocurrency. You can read about it here.
Coinbase seems to be one of the more "legit" sites I've checked out. I like that $10 signup bonus too, that's a particularly nice touch in my opinion.
I have not actually heard of Kucoin but I will definitely check that one out (you are now the second person on here to recommend it he he).
One of the bad things about Coinbase/GDAX is that they only have BTC/LTC/ETH/BCH, while Kucoin was many different currencies.