tough question because there are so many different answers...
the 1st thing that popped into my head was the age of the dinosaurs, if you will. being a caveman had to be interesting i guess, lol. running away from giant lizards and sabretooth tigers. never a dull moment.
then again, i have a tremendous amount of interest in ancient egypt. soooo, i would love to be the pharoah (sp?) who was in charge of overseeing the pyramids being built. (plus, it woulda been cool to talk with the aliens who assisted in building it, lolz)
last but definitely not least, c'mon, woulda loved to be dosed out on some high quality LSD @ woodstock with jimi hendrix. the whole hippie era totally melts my brain, because "reality" back then was on such a different stream of consciousness then it is now.
..............but then again, i guess that could be said for every era.
/rant