XCOM: Enemy Unknown will guarantee you a flat-top haircut that would make Guile jealous. Of course, we're talking about the classic blonde 'do from the original X-COM. It's part of the "Soldier Pack" that's included with pre-orders of all versions of XCOM: Enemy Unknown. Also featured in the pack are three new types of armor.
2K notes that the equipment is entirely cosmetic. That said, even if that haircut has no effect on rampaging aliens, it's bound to beguile anyone that watches you play.