The Subaru WRX uses the same pad as the GT.
Brembo uses pretty much the same caliper/design for almost all of their OE applications. It is the "F40" caliper. We offer a wide array of pads for the Ford GT. Everything from a good pad for daily driving all the way up to a made to order race pad. We used the race pads on the NZ rally, they take about three to four weeks to make. They will dust a lot and squeal, but the performance is amazing.
Also the front pads are the same as the rear pads.
http://www.stillen.com/browse.asp?c=BR&year=2006&make=FORD&model=GT
Kyle is right on. Race pads sound cool, but do not make good daily driver pads.
A. They need a little heat to start working well. Some compounds will increase stopping distance by a long amount when cold.
B. They are noisy, not real flattering for your supercar
C. Most are not as rotor friendly as OEM. They will cut nice little lines in the rotors.
D. They Dust like hell
E. When hot and on the track they work Very Well. Most will notice a quicker pedal response (bite).
Some are better than others. I would say the Hawk HPS is more friendly pad, but IMO not better than the stock GT pad. The Hawk Blues are pretty common track wear. These are nasty dusty and squeel like a cat, but work as advertised.
I got to the point where I just swap them in for track days and drive with the stock stuff on the street. This is not on the GT, but for other cars I have used for open track. I doubt the GT would be any different. I, like others in the Vet groups have switched to Carbotech over Hawk for the Z06. Better feel, bite and easy to modulate than Blues IMO, plus far more rotor friendly and a bit less dust. If you want the ultimate rotor grinder and stopping force, it's hard to beat the performance friction PF01.
Kyle may chime in on his favorite compounds for the weight of the GT. He has some mfg's that are pretty popular as well.