Regularly we get people on TSE asking what is the best phone/simcard for their upcoming travels.
As we do not do product recommendation, often the only useful answer would be a link to a site where they compare contracts and prepaid sim cards. But all of those I have seen do cover just one country, or even a smaller area or less wide range of options.
My main focus is on the Schengen countries and the UK/Ireland region, as that are areas where many people travel around and where countrywide options often only cover a few days of their travels.
A site which compares the 'travel Europe' deals for USA/Canada/Australia contracts would be welcome as well.
For international travel, a site that includes cheap rates in several European countries as search function would be very good.
Answers for other continents or groups of countries often traveled in one journey are welcome as well.