The spanish FreedomPop offers 10 GB monthly at €25, according to them valid in more than 25 countries without any roaming surcharge (confirmed in blogs of various users):
https://es.support.freedompop.com/ap...tail/a_id/2973
This could be an interesting data roaming SIM. I have not tried yet to order the SIM to an address outside of Spain.
It is a Three UK based SIM. Tethering seems to work on Android, however no tethering profile is available for iOS.