I just finished reading a manga named B Reaction by mangaka Tsuruta Hirohisa. A rather typical Shounen story with some ecchi stuff blended in, it is something like a cross between Kenichi and Tenjou Tenge and I was hooked for all 18 chapters of it.
The plot revolves around Onodera Kensaku, a 15-year old school kid who trains himself at "martial arts" by picking up street-fights incognito. He's good enough to win a local Karate tournament, but, as he's about to accept his award, he gets his arse handed to him by one of the cheer-girls at the arena. The cheer-girl in question also ends up being his new class teacher and Karate club sensei and things only go downward / upward from there.
Not the most original of stories, but there's a lot of humour, plenty of fights and a generous dose of ecchi thrown in to keep things interesting (and the pages always turning). Unfortunately though, it looks like the mangaka was given the boot and asked to finish the series early which results in the manga - which theretofore had been building up nicely - being wrapped up in super-quick fashion in the last two chapters which end up disappointing the reader, aka me :(
That said, fans of the genre will enjoy it very much. However, if you are planning on picking this up, I'd recommend stopping after the 17th chapter ... and saving yourself the heartbreak.