I just received the Scosche USBC242M from Amazon. It's fairly cheap, it's so small that the flap over the power outlet closes about half way while it's inserted and it puts out a true 2.4 Amps (12 watts) from each outlet at the same time. That's enough to charge a recent iPad at full speed.

I paid just under $14 for it, plus the usual reaming for postage because I'm in Alaska. (Foreign country fees, I'm sure. )

Too bad this isn't just built into the car to begin with, but I really like it. If you're looking for a small charger that blends in and has the most output current you can find I recommend this one.