The helmet I unlocked when I was promoted to lieutenant yesterday is the coolest one yet. It's reminiscent of a Greek helmet with its eye slits and cheek pieces. Compare those features on my new helmet, above, and King Leonidas' helm in "300."
I also learned an interesting tidbit about Spartans: they wore red cloaks so enemies would never see them bleed. The Spartan red was adopted by the Romans and later the British redcoats. I'm not sure if that's true, but it sounds plausible.
I've discovered a knack in Halo for splattering enemies with the Ghost. Look at this poor guy's neck and right elbow as I splatter him against a rock in Snowbound.