Just learned today that if you plop $35K in a bank account & give a bank passport to the DMV, you're considered financially responsibile for you own vehicle (and therefore are not required to have an insurance provider).
Probably not the best thing to do unless you're filthy stinking rich & can cover lawsuits and such, but if you are filthy stinking rich (or thereabouts) and have a fleet - this might not be such a bad option. You also get the benefit of no rate increase for driving poorly.
Case 2 for no insurance: If you have over 25 cars and are worth more than $500K (or so - maybe it was closer to $600K), you're considered financially responsible for yourself. You have to provide proof of income for the last 6 years and have to renew each year, but hey... If you've got the dough, keep it.
useless trivia fact #379.... and may only cover CA.
Virginia has something similar. You can pay a fee for not having the insurance and be responsible for paying for any damages. I don't know if you have to prove it or anything. Seems a little too risky to me, but I might look into it if I had a few billion to spare and didn't want the insurance companies to get rich off of me...
The principle of insuring yourself can be extended to those of us who are good savers but perhaps not stinking rich... just raise your deductible very high, and see your premiums come down. You don't want to make claims for small things anyway, so if you have the money in the bank to cover a $2500 or $5k deductible, you'll save a ton of money in premium reduction.
Of course, you'll have to evaluate whether you're a good risk. If not, my bet is the insurance company doesn't think so either and you're paying that money out one way or another.