As I'm sure I've said before, we have all of our property insurance with USAA. They are a solid company with excellent customer service and competitive rates. I've actually heard rumor that we could find lower rates elsewhere, though I've never checked.
If you are looking to comparison shop on your insurance, Green Panda Treehouse has put together simple directions for how to do it in her article How We Cut Our Car Insurance Bill In Half. She outlines the steps in a sensible manner to make sure that you are comparing the same kinds of coverage.
MSN Money also has a good article on Shopping for Auto Insurance, where they make the excellent point that "After a crash is too late to find out if your insurance policy is good enough." This is one of the reasons that I've stuck with USAA without looking at other options - I have had two fairly large car accidents and USAA has been super spectacular after each of them.
One more article I'll recommend is from Edmunds.com, the car sales people. Edmunds' thinks that car insurance shopping shouldn't be horribly boring because there is so much money to be saved. They have an excellent point there, and I'll add another: You only have to do it once in a while. Unlike clipping coupons or keeping an eye out for sales, selecting the right car insurance policy doesn't have to be done regularly to produce big savings.
I'm not likely to leave USAA anytime soon, but if you are considering using another insurance company, be sure to shop smart and make good choices for a balance between savings and service. Cheap car insurance that doesn't pay when you have a claim isn't a good value, no matter how low the premiums. You want a company who will give you quality service for a competitive price.