What cww said and short of adding the 20mm rear sway bar (highly recommended) from the STI you have the best factory suspension for the 5th gen. The 13' got stiffer springs, stuts/shocks, bushings and larger sway bars than the 12-down cars.
Lots of people are happy with H&R (who have a 2.5i and GT specific spring vs the 3.6r), Swift, Eibach, and RCE. other than RCE at 0.8", Eibach has about a 1" drop followed by H&R at 1.3" and Swift wich I think is 1.6". Then there are coilovers....