Just call and ask them to drop the rate, tell them you have another card giving you XXXX rate and then ask if they can meet it, if not tell them you'll just transfer your balance and use the other card. They've all heard the threat to cancel before and they know the game. The transfer threat is much more believable as it costs the cardholder nothing out of pocket to do it in most cases.
If they don't drop it, get a card that you can transfer to with a fixed rate on the transferred balance. AMEX Blue was doing it a year or so ago where your transferred balance had a 3% apr for the life of the balance. The catch is that these cards typically have a high purchase apr, and then they require that you pay off the transfer balance before any of the purchase balance. If you don't use it for purchases you don't get burned.
