I went with Clarion a year ago when I purchased my Series II. It was about $300/year for $13 - $14K of insurance.
I haven't (thankfully) had to make any claim against the policy, but when I was not satisfied that the policy language matched the verbal discussion I'd had in soliciting their services, they were quick to add a rider with the right info. Moral of the story: As with all financial and legal docs, give 'em a read.
I checked around with a few different companies at the time (can't remember names...sorry!), and Clarion seemed to have one of the better policies. Most will place limitations like, they won't cover the instrument if it goes missing after you leave it unsecured in public view (on stage???). Also, I had no problems getting them to cover replacement value. Plus, I was able to arrange that they cover the instrument from my point of pick up (BassNW, in Seattle). So, I was covered for the plane ride back to Alaska.
It seems to me that one of the sticky issues w/ most instrument policies was theft from a car. Clarion claims that they cover this, though I thought the language in the policy was a little squirmy on the topic -- I think that may have been the reason I got that rider. If anyone is interested in more details, I can pull out my policy and look it over.
Anyhow, based on my last survey of the field, Clarion seemed like the best available in the States. You can find them on the web at
http://www.clarionins.com/. One last and very nice thing was, they do musical instrument insurance. They are used to dealing w/ high-priced instruments (I recently heard that some cellos cost $100K!! Can you imagine?!?!), so unlike some places I spoke w/, the folks at Clarion were completely at ease when I told them I wanted $14K of replacement coverage.
Also, they offer things like Right of Repurchase, Borrowed Instrument Coverage, Newly Acquired Instrument Coverage, etc. Like I said, I've never made a claim, but the coverages sound good!!
Simon