Sekiguchi-ryu

Sekiguchi-ryū (or Sekiguchi Shin Shin-ryu ), is a Japanese martial art founded in the mid-17th century by Sekiguchi Yarokuemon Ujimune (also known as Sekiguchi Jushin).
He was a member of the famous Seiwa Genji Imagawa family, and when the Imagawa family fell to Oda Nobunaga, Jushin dedicated his life to martial arts training.
In the Atago Mountains he underwent physical and spiritual training and the result was the creation of Sekiguchi ShinShin Ryu.

Jushin was asked by the head of the Kishu Han, Tokugawa Yorinobu, to stay at Wakayama castle as a guest of the Han and teach Sekiguchi-ryū.
The art spread, but because of Allied bombing in World War 2, many of the historical documents and techniques were lost.
After 15 years, the art was restored and passed on till it reached the present day master, Sekiguchi Yoshio.

You can learn a lot more about Sekiguchi-ryū here:
http://www.bushinjuku.com/arts/bushinarts/sgrjj/sekiguchijj.htm

Nippon Kempo

Nippon Kempo was developed in 1932 by Muneomi Sawayama, although the origins can be traced back to Nomi no Sukune and Taema no Kuehaya, the founders of Sumo Style Wrestling. Sawayama was a student of Okinawan Karate Master Kenwa Mabuni, founder of Shito Ryu.
Nippon Kempo is a Japanese martial art that places emphasis on striking techniques using hands and feet, immobilization and controls, projections and take-downs equally.
Although it is a system unto itself, it also uses techniques from other martial arts, including judo, jujutsu, aikido, karate, and wrestling.
Practitioners practice these techniques with protective gear (bogu kumite).
Nippon Kempo is practiced in universities in Japan, and is also part of the training in many police forces.

To learn more about Nippon Kempo you can visit their website here:
http://www.nipponkempousa.com/

Ninjutsu

Ninjutsu is the martial art, strategy, and tactics of unconventional warfare and guerrilla warfare practiced by the shinobi (ninja).
Of course the tales of Ninjas are widespread and all over popular media from video games to comic books to movies.
The invisible, silent assassins are seen everywhere.
Kind of defeats the whole idea doesn't it?

Ninjutsu was developed by people mainly from the Iga Province and Kōka, Shiga of Japan.
All through history the ninja have been seen as assassins, scouts and spies, noted for their use of stealth and deception.

Ninjutsu was developed as a collection of survivalist techniques that included gathering information, techniques of non-detection, avoidance, and misdirection, disguise, escape, concealment, archery, medicine, explosives, and poisons.

The lineage of modern day Ninjutsu schools is very cloudy.
Most modern schools are considered "Neo-Ninja" because of this.

I am in no position to argue the validity of any of the modern schools claims.
So if you are thinking of studying Ninjutsu you need to do a lot of research on your own.

Nanbudō

Nanbudō is a relatively recent martial art, founded by Yoshinao Nanbu Doshu-Sōke in 1978.

Nanbudo's roots are in Karate, but it is considered as an independent system.
It is more than just fighting techniques.
Nanbudo is based on four concepts: breathing, energy manipulation, gymnastics and spirit/ mental strength.
The techniques are based on movements and patterns in nature, and are intended to work as a system to strengthen the body, as well as prevent many modern-day illnesses.
The fighting techniques in Nanbudō include punches, strikes, kicks, throws, locks, joint and pressure point techniques, and grappling techniques.
Most of the techniques are unarmed, but Nanbudo also uses the bo (six foot staff) and bokken (sword).

For more information, you can visit the Nanbudō website:
http://www.nanbudo.com/

Naginatajutsu

Naginatajutsu is the Japanese martial art of using the naginata.
The Naginata is a a pole weapon with a curved blade on the end.
Not very practical in today's world as far as self defense goes, but still a great discipline and a very graceful martial art.
Of course since the weapon is so simple, there are several theories on how it originated.
Some of the theories are it was a modified farming tool, a Japanese modification of a Chinese Guan Dao or an inventive samurai needed a longer weapon, so he attached a sword to a pole.
The weapon was originally used against opponents on horseback, allowing the user to stay a safe distance from a mounted opponent.
Naginatajutsu is today most often practiced in the form of a sport called Naginata.
For more info you can go to the All Japan Naginata Federation here
http://www.naginata.jp/
Or if you can't read Japanese, you can go to the International Naginata Federation here
http://www.naginata.org/inf/inf.html