The HCl bonds strongly with the surface moeities on the GO surface, so it is difficult to neutralize GO after the Hummer's method. Your best bet is vacuum filtration with repeated washes of H2O, and vacuum drying of the paste at around 40C to prevent partial reductions due to acid-catalyzed dehydration.
The drying procedure is very important to maintain quality of the GO sheets, as those dried at high temperatures can pi-stack to reform multi-layer graphite, i.e. they will not be easily water-dispersable.