I just wanted to add another style that is heavily influenced by Hapkido. It is called Hapmudo and was founded by Grandmaster Yong Sung Lee. It is a mixed martial art that is still very focused on traditional aspects. The website is: http://www.hapmudo.net/
-- On a side note, I have been studying this style for around three years now and I really like it. Hope this helps ^_^.
Proud student of Grandmaster Yong Sung Lee, founder of Hapmudo