I'm only looking for the prepaid data sim cards as a traveller:
France: free.fr 10 euro sim card out of a vending machine. For 20 euro per month you get up to 50GB if you are only using 4G. On 3G with a 4G device it's 20 GB. There is 35 days of free roaming per year, 3GB on 3G. Their network is expanding and are reducing the reliance on domestic roaming on someone else's 3G network. Brilliant for travelling through France and neighbouring countries.
Netherlands: Vodafone 10 euro online only bundle 4G 1GB domestic and 1GB domestic/roaming. 1 euro for 1 day (100MB LTE) usable in anywhere in Europe. Brilliant if you cross the border like a dozen times a year and spend a dozen euro on it without having to own German, French,... sim cards. I spent like 10 euro a year on them.
UK: O2 ticket presale, £ 1 pizza lunch, free bottled drinks (Quite useful in London were the small grocery shops at prime locations are asking gas station prices.), skipped queue at Brixton,... and rural LTE coverage. I'm getting much more out of it than I spent on it. I probably spend £ 10 or maybe £ 20 in last 5 years.
It's Kat friendly (£ 1 pepperoni pizza on Mondays included).
