Did you know that recent changes to the law require credit card companies to apply any payments in excess of the minimum payment to balances with a higher interest rate? Say you have a balance that had a promotional rate applied to it (i.e. 0%) and also a balance with a normal interest rate (say 15%). If you have a minimum payment of $50 but instead pay $150, the extra $100 must be applied to the balance with the 15% rate, thereby saving you money.
Always a good idea to check your credit card statements and make sure this is being done. While I have not caught a credit card company not doing this right (yet), I recently saw a comment on one of my credit card statements by the credit card company bragging that they apply your excess payments to the balances with the higher rates. In other words, they were bragging that they follow the law. That's like bragging that you didn't murder someone today. Which, if you've dealt with certain credit card companies today (Bank of America springs to mind), refraining from murdering someone might be something worth bragging about!