I'm apparently crazy. I like extensive house rules and make a bunch of them myself so you might want to take these with large grains of salt.
Helmets are awesome! I don't think they get the respect they deserve in d20 games. So my theory is that armor slows you down but protects the squishy bits behind it.
Light Helmets; -2 Perception/Spot&Listen, Grants DR 1/-, this includes skull caps, chain coifs, and those horny helmets vikings used.
Heavy Helm; -5 Perception/Spot&Listen, Grants DR 2/-, including great helms, houndskul's, hoplite helms, and sweet biker hats.
Armor if you care works along similar lines, it slows you down but saves your butt.
Light Armor; -1 Ref(Saga)/AC+Ref, Grants DR 2/-, this includes boiled leather jerkins to light mail.
Med Armor; -2 "" "", DR 4/-, Breastplates, scale, hide.
Heavy Armor -3 etc, DR 6/- Full plate and Beyond!
So a heavily armored knight can hardly see the ambush coming and is harder pressed to get out of the way carrying an extra seventy pounds of gear about, but he is almost literally a tank and can weather some truly fearsome strikes.
This obviously won't work for everyone one, but it works out pretty well for me and mine.