What about giving the fighter something akin to a specialist school or domain similar to Alpha 2's Wizard Specialist schools or the Cleric's Domain powers?
The first ones that come to mind are the weapon & shield, 2-weapon fighter, 2-handed fighter, archer, and light fighter.
Each specialist school could be given abilities at each level just like domains and schools do for said casters.
Just throwing it out there.
My recent post suggests something along those lines.