Greece

Greece
There are apparently three operators in Greece offering mobile broadband: Cosmote, Vodafone and Wind.

Cosmote
Cosmote plans (Google translate)

Despite saying prepaid, it needs to be checked whether this is acutally PAYG.

Vodafone
Vodafone offers a PAYG sim called KartoInternet

The €20 for the SIM include 10 days of internet, further prices are listed on the webpage.

Wind
I could not extract nothing from Google translate.