I use Banfield. Petsmarts insurance currently. They are pretty good. I am going to be looking into other insurances as well. as I would like to go back to useing my family vet..not that I dont like banfield. they are nice but i miss my family vet!
I'm in sweden so the company isn't all that relevant but we got a medical policy for our kitty quite cheap because we have house insurance with the same people. Could be something to think about asking for.
I tried it once in the UK, but it cost a lot and then when my cat got sick I found that the condition wasn't covered. So now I just make sure I put enough away each month to cover all regular shots/exams etc and a bit extra for emergencies. And in a savings account I get interest on it too!