I insured my Tiger Super Cat with a firm called CIC. They were (at the time) a lot cheaper than the other insurers such as Footman James and Adrian Flux. Their renewal quote was also very good. However I didn't have to make a claim, so I can't vouch for how good they would be in that instance!
I think mine's pricey, because I'm younger than everyone else, it's the Type-R engine, I haven't got a clean licence (whooopsie), and I've got the highest mileage.