I'd go with something cool if it were me. If there were enough of you, I'd suggest going as the guys from Resovoir Dogs - suits, sunglasses, etc. Refer to each other as Mr. White, Mr. Brown, Mr. Green, etc. Refuse to come out of character.
Or you could go as the people on Nixon's enemies list. Most of your classmates wouldn't go for it but your teachers would love it - you'd almost be assured of getting an A in history.
Or you could go as a twist on another well known group. Instead of going as Jesus Christ, you could go as Jesus Christ Superfly. You'd need a nice white robe, sandals, an afro, and a gold cross to snort off.