Different aikido styles, teaching methods and organisations began to appear during the later years of O'sense's life and exploded in to existence after his death, here's a list of the more known styles and affiliations
Aikikai
The largest aikido organisation, and is led by the family of the founder. Numerous sub-organisations and teachers affiliate themselves with this umbrella organisation, which therefore encompasses a wide variety of aikido styles, training methods and technical differences.
Prominent sub-organisations include numeral national Aikikai, as well as several US based including United States Aikido Federation (USAF) and Aikido Schools of Ueshiba (ASU).
Yoshinkan
Founded by Gozo Shioda, this branch has a reputation for being the most rigidly precise. Students of Yoshinkan aikido practise basic movements as solo kata, and this style has been popular among the Japanese police.
The international organisation associated with the Yoshinkan style of aikido is known as the Yoshinkai, and has active branches in many parts of the world.
Yoseikan
This form was developed by Minoru Mochizuki, who was an early student of O Sensei and also of Jigoro Kano at the Kodokan. This style includes elements of aiki-budo together with aspects of karate, judo and other arts.
It is now carried on by his son, Hiroo Mochizuki, the creator of Yoseikan Budo.
Shodokan Aikido
Often called Tomiki aikido, after its founder Kenji Tomiki, this style use sparring and rule based competition in training as opposed to most others. People tend to compete to train rather than to train to compete. Kenji Tomiki, an early student of O Sensei and also of Judo's Jigoro Kano, believed that introducing an element of competition would serve to sharpen and focus the practice since it was no longer tested in real combat.
This latter view was the cause of a split with O Sensei's family who firmly believed that there was no place for competition in aikido training. Tomiki said that at no point did O Sensei actually cast him out.
Ki Society
The Ki Society, founded by former head-instructor of the Hombu dojo 10th dan Koichi Tohei, emphasises very soft flowing techniques and has a special program for the development of ki.
It also has a special system of ki-ranks alongside the traditional kyu and dan system. This style is called Shin Shin Toitsu Aikido (or Ki-Aikido).
Iwama Ryu
Iwama Ryu emphasises the relation between weapon techniques and barehand techniques, and a great deal of emphasis is placed on weapons training. Since the death of its founder Morihiro Saito, the Iwama style has been practiced by clubs within the Aikikai and an independent organisation headed by Hitohiro Saito. Saito sensei was a long time uchideshi of O Sensei, beginning in 1946 and staying with him through his death. Many consider that Saito sensei was the student who spent most time directly studying with O Sensei. Saito sensei said he was trying to preserve and teach the art exactly as the founder of aikido taught it to him. Technically, Iwama-ryu seems to resemble the aikido O Sensei was teaching in the early 50s mainly in the Iwama dojo. The technical repertoire is fairly large.
Iwama Ryu Aikido, currently headed by Saito Hitohiro, is a separate organisation from the Aikikai. The Iwama Dojo is currently affiliated to the Aikikai and is not considered a separate style. Many instructors who were deeply influenced by Saito Morihiro consider themselves Iwama Style, however.
Shin'ei Taido
Founded by the late Noriaki Inoue, nephew of Morihei Ueshiba. Noriaki Inoue.
In his early years Noriaki Inoue closely associated with the spiritual and technical development of aikido along with his uncle Morihei Ueshiba. Shinwa Taidō later became renamed to Shin'ei Taidō.
Yoshokai
Yoshokai aikido, begun by then-hachidan Takashi Kushida-sensei of Yoshinkan aikido, is a remarkably centralised style of aikido, with test techniques yearly passed down with explanations from the home dojo.
The syllabus contains a considerable amount of weapons study, and like Yoshinkan, Yoshokai includes many solo movements and exercises.
Tendoryu Aikido
Founded by Kenji Shimizu. Kenji Shimizu. Shimizu was born in 1940 in Fukuoka, Japan.
He had been training judo since childhood and held a 4th dan in this art when he changed to aikido in 1963. Tendoryu Aikido is characterized by its large and clear movements, emphasizing naturalness and harmonic flow of motion.
Shin Budo Kai
Shizuo Imaizumi, born 1938 achieved a 7th dan in Ki Society aikido. He broke away from the Ki Society in 1987 and founded the Shin-Budo Kai style of aikido. The organisation was officially created on October 1 1988.
Shin-Budo Kai is independent of both the Aikikai and Ki no Kenkyukai with Imaizumi serving as Chief Instructor. Shin-Budo Kai's emphasis is on knowledge provided not only by aikido, but on other martial arts and in Genkido; ki-exercises.
Kokikai
Kokikai aikido, founded by Shuji Maruyama in 1986, focuses on minimalist but effective technique. It emphasises natural stances and ukemi that do not require high breakfalls, and de emphasis es atemi and techniques that cause pain or undue discomfort to uke.
As such, it is considered by some to be a "soft" style of aikido.
Seidokan
Headed by Rod Kobayashi. Tends to utilise movements which are very small and economical.
Encourages students to discover an aikido which is truly their own, stresses the importance of doing away with the extraneous and focusing on that which works.
Nippon Kan
Headed by Gaku Homma. His early career as a teacher was on a US air force base. In 1976 Homma moved to Denver, Colorado, and founded the Nippon Kan as an independent dojo in 1978.
This dojo has grown into the largest aikido dojo in the Rocky Mountain region and is well known for its international uchi-deshi program. He has organized several large aikido seminars in Denver, many of them taught by Saito Morihiro.
Nihon Goshin Aikido
Founded by Shodo Morita who had mastered Aikido, Karate, Aikijitsu, Judo and many weapon arts. He was highly respected by senior members of the martial arts community on the northern island of Hokkaido, Japan.
His school was located in the town of Chitose. Current director, Mr. Richard A. Bowe, studied under Master Morita in Japan and brought the art to America in 1962.
Tenchin Budo Kai Aikido
Headed By Frank Ani Jr. This is a "hard" style Aikido, combining the basics of Tenshin and general Aikikai styles together.
It also includes techniques from Aikijujutsu making it a very practical and street effective version of Aikido. Only a few qualified instructors teach this style of Aikido. This style is an independent style with no affiliations.