An Introduction to Wu Style, Wu(Hao) Style and Sun Style Tai Chi
There are in fact two different styles of Tai Chi named Wu created by different teachers.
Both were inspired by Yang Style Tai Chi although Wu(Hao) recombines techniques from the Chen tradition.
Wu Style Tai Chi
Wu Style focuses on smaller circular movements of the hands in addition to the large ones in Yang Style.
The story goes that Yang Lu Chan's son, Yang Banhou only taught Wu Quanyou the large circle movements within Yang Style and so was always able to beat him easily in Pushing Hands practice and caused him to go lame in one leg.
Yang Lu Chan saw this and decided to teach Wu Quanyou, the small circle movements himself and afterwards Yang Banhou was never again able to beat him.
Wu Quanyou went on to form a new form of Tai Chi Chuan, which focused directly on the small circle movements and this became Wu Style.
Wu(Hao) Style Tai Chi
Wu(Hao) was created by Wu Yu-hsiang who learnt Yang Style with Yang Lu Chan and probably Chen Xiao Jia with Chen Chin Pin.
The main lineage holder appears to be Liu Jishun who now lives in California, but his teacher Hao Shaoru taught many students in China in his life and so there are no doubt many good people to learn with there.
Sun Style Tai Chi
Sun Style Tai Chi was created by Sun Lutang (1861-1932) who was an expert in Xingyiquan and Baguazhang and then went on to learn Wu(Hao) Tai Chi with Hao Weizhen. Apparently he also had contact with Yang Shaohou, Yang Chengfu and Wu Jianquan. (Source Wikipedia)