you could go as Professor X , or Captain John Luke Pickard, Daddy Warbucks, Yul Bryner, etc.
or you could do some cool things with some partial hairpieces. you could get that mohawk you always wanted and go as the guy from taxi driver.
or you could get the hairpieces necessary to go as a Japanese samurai of the feudal era - they shave the entire tops of their heads and then took a top knot from the back of the head, folded in half, and laid it halfway over the top of their heads