The 12-volt adapter in a car is nice for radar detectors and GPS devices, among other non-cancer-causing activities. But this inverter can use the ciggy adapter to power USB and AC stuff, up to a claimed 120 watts.
It works well, too.
I had it charging a Sony Ericsson by USB cable, and also powering up the monster 85 watt MacBook Pro powerbrick while both devices were active. But not at the same time. The USB cable didn't want to charge the phone while the MacBook was gulping down juice. The inverter also hummed away, like an overhanging power line ready to zap a pigeon. The solution? I charged the USB device from my laptop. I'm sure the USB wouldn't flake out if I'd used a less demanding AC device. (Not a space heater.) Bonus—it's a three-pronged adapter.
The manual does a good job of outlining the dangers of using your car battery for this sort of thing. They recommend for every three hours of use, starting your car and running the engine 20 minutes.
I give this thing a thumbs-up at $40 from Think Geek.