I purchased a 3rd party warranty through a dinky site for my Porsche 911-- InsurancePoliciesOnline. Like I said, the site is pretty dinky. So when I originally bought the poilcy, I paid with my AMEX just in case... but it ended up being just fine.

I bought the 4yr, 50,000 mile platinum coverage with $0 deductible for a little over $2400, and it was honored at every Porsche stealership I took the car in to for service. I had everything from a broken fuel tank cap to a motor rebuild paid through the warranty. In total, the policy probably paid out over $20k in repairs for the $2,400 I paid. Unless you're dealing drugs, I doubt you'll get that type of ROI anywhere.