While your car is still registered in another state, keep the insurance that is valid for it in that state. Best advice: phone the number below, chat with a broker and ask him/her -- they'll know the up to the minute regulations.
This is my agent. I've used them since, ummmmm trying to remember now, I think 1988. They are brokers who represent a choice of insurance companies. They're in Bellevue, but given phone, internet and email it doesn't matter where they're physically located. They are well reputed among individuals and businesses in this area. I use them because I have a few types of insurance (including homeowners, etc.) folded to reduce the premium. If you're looking for auto insurance only, perhaps Progressive online will be less expensive.
Arthur J. Gallagher & Co.
225 108th Ave NE # 500
Bellevue, WA 98004
(425) 454-3386
Arthur J. Gallagher & Co. Home Page