I've been told my credit rating is actually hurt by the fact that I have only one credit card and no loans or other forms of credit. The fact that I've never missed a credit card payment is apparently not entirely relevant (though it does at least keep it up to a decent level).

It's weird. I'd need to take out some kind of loan that I don't need, to get my credit score up in advance in case I do need it at some point in the future.