Another trick, knotted -- sometimes if you call and tell them you're switching to a lower interest lender, they'll lower theirs (at least temporarily) to keep you.

Also, don't be late on your payment, because most of them have written into the contract that they can raise your interest rate if you do.

Oh, another thing -- check with your bank or credit union. They may let you transfer your balance to them at a lower rate. (Then don't touch the Visa until you get the other paid off, natch!)