Aerodynamics - Cervélo - 80ish % is the rider
Updated - EB14: Cervelo Ups the Aero Road Ante Again with a New S5, plus Updated RCA - Bikerumor - 30ish % of the 20% that is the bike, is the bar.

Let's pretend the above linked data is gospel. Relative to the full rider/bike system you get the following drag percentages:
Bars: 6%
Front Wheel: 3.2%
Frame: 3.2%
Fork, Bottle, Drivetrain: 1.8% each
...etc...