I used to use Nationwide CC (as stevelup said, it is free of the commission charge - typically 2.75%). I now use Abbey Zero which is also commission free - I had a lot of problems with the Nationwide CC being suspended without any warning when I tried to make certain purchases (French SNCF rail tickets, Mobile phone topups for example). The Abbey Card seems free of these "issues."
I believe there is also a CC issued under the UK Post Office which is similar to the Abbey one.
Other Comments (I stand to be corrected on any of these!):
I'm not particularly up to speed with the legal side but I recall that the protection mentioned (£100 - £30k???) is only law with regard to spending (ie contracts made) in the UK (I think that most providers add worldwide cover voluntarily, to their contracts though).
BackPacker mentioned putting the CC into prior credit. Again I suspect that the user is still "protected" from loss by their contract terms but I think the basic cover under the Consumer Credit Act is not applicable because whilst the account is actually in credit (literally) it is not strictly being used to obtain credit (and therefore outside the scope of it). (Vice versa, in a similar way, I understand a current account which is overdrawn also "enjoys" purchase protection under the same statute).