I am actually designing the Prestige Class myself, and I am looking for inspiration for class abilities and feats that fit the concept. So far, I have a tactical unit fighting ability, precision-based damage, iron will and a level-dependent armor bonus, because I want them to use light armor.
Most of the Prestige Classes the game offers are too mysterious or magical or do not fit the concept. Basically, they are an elite fighting force much like Delta.