Currently i have:
6 terminals (out of 8, or 7 if you're only counting the Marathon Man ones)
10 Skulls (you really DO have to start from beginning of levels to get skulls. as i found out the hard way)
And Armour Permutations:
different feats and achievements (feats like getting 750 gamerpoints or unlocking all H3 achievements) will get you different pieces of armour
the coolest spartan armour is Bungie-related people GIVEN to them.
for Hayabusa Armour ther is a FOURTH piece unlocked by getting all H3 achievements (its a katana on the back)
Other armour are unlocked :
Head , Chest , Shoulder (though you can mix'n'match shoulders, each "set"'s shoulder is unlocked separately)
Also, there isnt always 3 pieces for all the sets, some just have head pieces or other ones |