If you really want to improve your braking, get a big brake kit up front and ssbl's all around. Since you have a GT, you might think about a rear-disc conversion however the front does 80% of the braking anyway so you'll have to weigh that choice yourself.
If you only want rotors and pads, you can try Brembo, Stoptech, and Rotora for larger rotors and I prefer TRD for my brake pads... but don't forget to upgrade to ssbl's regardless of which option you choose -