My many colleagues are doing some sterling work in terms of research and provision of quality information, it seems pointless to repeat it, so below I have included some links to sites that are useful for my students. Additional sites are listed under the links page. Here is my small contribution:

The Wu Dang Style is descended from classical Yang through Yang Ban Hou, and classical Wu after Wu Quan Yu and Wu Jian Chuan ( I believe the latter was responsible for developing the square form, I read this I think in Pa Kua Journal in the 1980's, but have since failed to find any sources to confirm it, I will keep trying) Cheng Tin Hung established a reputation for himself, and his interpretation of the style as an effective martial art , hence the name Practical Tai Chi Chuan, bestowed by journalists. His students and subsequently theirs also, have continued to uphold the reputation by winning many international competitions.

In terms of appearance, the Wu Dang Tai Chi Chuan hand form can be said to be a medium frame, medium pace form, with tremendous use of the waist and an obvious inclination in forward stances as a result of the 100.% weight separation (unlike the more usual 70/30 or 60/ 40 stances of other styles) never the less correct alignment of the spine and use of total body force should be clearly in evidence, as should coordination, smooth flow, and all of the usual qualities of good Tai Chi..

The outward appearance is something I would describe as purposeful, structured, precise yet relaxed; weapons forms from this system are in my opinion some of the more beautiful of any I have seen..

The practice of Wu Dang consists of five main areas (described elsewhere) I believe that those who practice all aspects develop more fully as Tai Chi practitioners.

Lineage - link to chart by Norman Jones.

Overview - link to Wikipedia entry

Practical Tai Chi Chuan International -link to Dan Docherty's site

competative scene -link to Wim Demeere site here

or

Niel Rosiak site here

Please see links page for additional Wu Dang and other links

(Tai Chi the supreme ultimate, Chuan literally fist, meaning method of fighting)  
Rooted in Taoist philosophy, and health practices, stretching back beyond recorded history, Tai Chi Chuan (often shortened to Tai Chi) has developed a proven record of success in restoring health and promoting vitality. One of a small number of ‘Internal ‘or ‘soft’ martial arts. The success  of Tai Chi Chuan is a direct result of its foundation on the principles of Wu Chi (no ultimate) Tai Chi (ceaseless change) Yin and Yang( the two principles) Wu Wei (not against nature) and other touchstones of Taoism.

Yi (intention) leads the Chi (intrinsic energy) and the body moves
This approach dictates that the spirit is raised, the mind remains calm, and the body used according to its inherent principles, tapping into and developing intrinsic energy, rather than relying on brute muscular strength.

Whole body exercises
When we practice ‘Chinese internal arts’ we develop the subtle interface between body and mind, using our intention to lead the body through a series of carefully designed attitudes, that stretch and compress, twist,  turn, open and close all the joints, muscles and ligaments. Improving and developing essential circulation whilst promoting a new understanding of fundamental movement that is without strain or wasted energy.