In reply to focus89uk:
If you can afford the penny's, go for the Petzl Frieno carbiner. It was designed to go with it after all.
If not then any screwgate one will be fine, It does not have to be a HMS as the rope is not in contact with the carbiner. I however actually use a Clog HMS, as it allows the Grigri 2 to sit a litle bit higher when I belay wearing my lightweight harness (loopo)