I study several systems and need some month or years to go deeper into each of them, I try to not mix them because my test have prove that is counterproductive for most of qigong even if it is still possible to find a good combination on daily basis. Most of the qigong dvd offered are not produced by true lineage excepted few and among the best ones have already be given into this topic.
I have myself found high value into the reading of each message here. As we speak about potent systems I think that Qinway Qigong dvd is powerful and effective as it is easy to do and send energy signal transmission to the practicer, it is called recharge qigong so it has a great value regarding health,rejuvenation, cleasing and activation of energy systems. It is also very good to add the yin yang tea for few month and perhaps to wear some energised items all the time like a pendant to keep the signal always near the body. Another one is Pangu who is very strange and very easy but has great effect if done everyday during at least 6 month in a row and I think that is good to read the 3 books about Pangu " The path of life" as it is a way to receive the energy transmission also the calligraphy of Master Ou give high value energy who help healing and spiritual awakening. Another form is Falun Gong but I cant say anything about it as I have choose to follow other path. Yan Xin qigong a great one and among the most advanced form need to receive energy activation from a recorded lecture of the NINE STEPS ( easily available at this time), great but need time and dedication.
Fragrant Qigong is very potent system even at level 1 it can help health and spiritual evolution, at level 2 psychic/clairvoyance can occur. I think that is best to practice one session in the morning and another one during the evening without obsession. Master Tian family send Fragrant water empowerment everyday to help every practicer and even non practicer of Xiang gong.
There is also the Quan Yin Magnetic Qigong from Wu Lao Xie who can be of great help.
Recently I have also start to study the Gods Playing in the Cloud Qigong who seem to be a true lineage Qigong with a deep teaching.
I dont know if there is other easy but really potent qigong out there but these ones have great value if done on daily basis. Also it can be good to try each of them during 3-6 month and write the feeling, experience, effect. Then after the testing process the best and wise way is to choose only one and stick to it.
Tao Stilness have perhaps tried too much systems or from different tradition and have locked some energetic circuit into the body. I suggest to unlock them first before to do anything else. Perhaps a good master can do that for you.