I use a sleepy pod.
http://sleepypod.com
It isn't a car seat so much as a carrier. But it belts into the car and has been proven in crash tests. My girls travel with me all the time in the car, both on road trips and trips to the cottage. I feel so much safer...and Charlee loves the carrier, jumping in as soon as I open it. The bottom zips off to create a separate bed. I got Charlee used to it by starting her in the bed then adding the top, then short trips before long trips. We are leaving next week for our first plane trip and I'm happy that Charlee already is so comfortable in her sleepy pod that the new form of travel should be a breeze! Fingers crossed��