This may appear like going to the extreme to save money but if it works it's worth a shot. According to a certain blogger, if you've been using a specific credit card for a long time, you can call the issuers and threaten that you'll be dealing with rivals from then on if they don't lower your rates. How you do it doesn't matter [be it using diplomacy to negotiate for lower rates or the previous more straightforward methods]. Question is, does this work?
The rate that you are offered on a credit card is based loosely on your credit score. If your score has improved over time because you are reliable at making payments, you should be able to negotiate a better interest rate. Having said that, If you are paying interest on your card, you are not saving money. In order to save the most money, you need to pay off the balance in full each month. If you do this you will accrue no interest charges and the rate on the card won't matter. Yes, you can negotiate a better rate to save some money, but paying any interest at all is costing you - plan ahead and spend only what you have.
Like Lostvalleyguy said, if you pay any interest you're almost certainly losing money. However, there is one very rare case where if your interest rate is low enough and you can invest money at a higher rate, then you can potentially come out with a profit - but this is extraordinarily unlikely with credit card APR, which are usually at least 10%+, while even the more high risk investment opportunities make somewhere between 7-10% on average.
I imagine most credit-card people would be like, "Okay, whatever works for you See ya Don't let the door hit you on the way out!" Maybe if you've been with `em long enough to be on their level of "doing business," you can 'negotiate' (tell `em "I'd like to keep on using your card, but this other card is offering rates of x% ... any way you could gimme rates lower than that?" ... prob`ly not, but never hurts to ask ... maybe even demanding to 'speak with a manager' first.) Just to be clear here (with you & all the other responders here): 'The reason you pay CC-companies their interest-rates' (the way they "earn" the interest) is because THEY pay for the stuff you get with your credit-card ... sure, YOU get the stuff directly from the seller, & the CC-company doesn't even TOUCH the stuff (unless they're delivering it); but THE MONEY TO THE STORE comes directly from THE COMPANY's account, and so you owe it (plus interest) to them.
@Denis Hard I don't think this will work in my country at all where rates are uniform depending on the credit card type. However, I can call them to reverse annual fees which I always do. In my country, the lowest credit card rate is 2% per month, the rest have similar rates of 3.5%. In other words, I can't possibly threaten to leave them for another credit card provider with a lower interest offer.
I haven't heard about this credit card deals. But we always look for special offers from banks stating that they will pay all our credit card debts with 0% interest. And we pay them within 14-16 months. It's really a big help for us, esp. when we have emergency expences and we have to use our credit card.