I used CARS UK to take the Volvo to Beijing. Pretty much compulsory because they have the warehouse facilities etc for picking the car up there. They were very good: picked the car up from home and after the event delivered it back. Excellent service, but at a price.
I've also used Schumacher to bring a Corvette in to Australia from Colorado. No complaints there: I would have used them again to ship the rally car back from Paris, but they didn't service that end. If you are going somewhere they service, I'd recommend them.
Good luck with the shipping - its a bit of a bureaucratic nightmare, especially if you plan to bring the car back.