I do Shorinji Kempo. Not related to any other Kempo forms as far as I know, but it's my favourite.
Why choose this one?
I looked at many martial arts before and took [a form of] Karate before, but found it quite impractical; more of a discipline than something I could really use to defend myself. I needed something that really made sense to me.
I found the basics of Shorinji to be very practical and based upon commonsense. Having a very athletic background I found that it utilized all of the principles which I innately learned over the years doing all kinds of different sports. I see it as really no different than something such as tennis, in that that same principles of physics, kinetics, leverage, etc. are the same.
The more advanced techniques are very interesting and challenging and neither size nor strength matters in their execution, but speed, skill, and accuracy are needed. This is what first drew me to Shorinji, as I was amazed at how using such little strength, only leverage, I was able to easily take down a much larger and stronger person.
The philosophy, having roots in Buddhism, focuses on teaching love, respect, humanity, peace, and decorum. The teachers are all volunteers and it is a non-profit society. Therefore, fees are low, there are minimal belt colours (3), and students can be on the board and be involved in the decision making and financial management etc.
One aspect of Shorinji Kempo that is different from any other martial art [that I know of] is that it is a world organization. This means that the teachings are all centralized at the office and teaching headquarters in Japan which allows a standard to be maintained worldwide. It also means that your level of education and belt ranking will be undisputedly recognised everywhere. Headquarters also functions as a Shorinji Kempo school where one may enrol for more intensive training learning straight from the top ranking teachers.
It’s not a famous martial art, but I believe it’s now in 32 countries; widespread in Japan, it is taught at most high schools and universities; there are at least a couple thousand dojos in Japan as a result.
Anyway, I wrote a few tidbits about it here:
http://www.bestbread.ca/shorinji