Kukkii-san 'Poofy' ponytails never get old for me! In addition to foamcore, this one is supported by a superstructure to keep it from sagging, despite having a narrow base (sort of a bottleneck shape).

Tutorial: http://www.cosplay.com/photo/3445695/

1 mid-length wig, extensions x4 (27 - strawberry blonde); foamcore, superstructure