Serious Sam HD: The First Encounter, Serious Sam HD: The Second Encounter, Serious Sam 2, Serious Sam 3: BFE, Serious Sam Double D & Serious Sam: The Random Encounter, PC – £6.18
Registers on Steam.
To purchase digital games from Amazon US, use your UK Amazon account, and add a US billing address to your account. This address needs to be a valid US address, but nothing will be sent there, and you can access all your games through their website. Some card issuers may charge a fee.
Cheers Ben for the tip off.