we have both our cats on 4k moggie insurance with petplan. which i think is adequate.
Our cat boog was very ill with nasal lymphoma and her bills came to ~£3500, which included normal vets bills and RVC bills for xrays and investigations etc and included the bill for putting her down.
i thought it was very reasonable, easy to claim etc they even said i could pay just one excess payment even tho i should have paid 2. They were very helpful and the girl i spoke to after boog was put down seemed genuinely upset!

lol
There was a problem with them receiving my claims, they say they didn't get them and the vets definately sent them in the end they were sent 4 times to make sure they had it, but i think that's cos they have soo many bloody fax machines that it got lost. Anyway that was all sorted and didn't affect the amount i got paid back.
I would recommend them over someone like a supermarkets insurance etc.
I would choose the amount of cover depending on your area, if you live somewhere quiet and the cats unlikely to get run over, like our area then go for one of the lower ones, but if your near a main road etc go for the higher cover.