Originally posted on 07/16/2018:
It will depend on your country.
Go here: https://www.sportsbookreview.com/betting-sites/ and select your country in the left column.
You will be looking for names 5Dimes, Betonline, Youwager, Bookmaker.eu/BetCRIS.eu, The Greek, Intertops, Jazzsports as the main books focusing more on American sports.