The National Association of Insurance Commissioners puts out an annual report tallying auto insurance premiums and other data, state by state. (Here's the link, but note that the report costs $200. Our agency belongs to the NAIC, so we got a copy for free.)
So how does Washington compare? A little higher than average, but definitely in the middle of the pack. The national average for auto insurance coverage in 2007 was $912. Here in Washington, the average cost was $928.
The lowest average cost, it turns out, was in Iowa, where auto coverage cost an average of $620. The highest-cost state was Louisiana, at $1,262. Washington, D.C. was even higher: $1,289.
The 260-page report breaks down premiums by state in far more detail: different kinds of liability, personal injury protection, uninsured/underinsured motorist, etc. etc. It also has car-wreck fatality data (Washington's one of the lowest), average car-repair cost per claim ($2,366, which is about average), car-theft statistics, road miles, and other information.