Which martial art for KO's and quick take downs?

Hey guys. I'm really looking to do something different, exciting, yet useful. I've decided a martial art would be just the thing. I've had some experience with Tae Kwon Do and I don't find it enjoyable or useful. In short. I'm looking for a martial art that specializes in quick take downs and KO's. I've heard there is an art where you KO people using pressure points? What art is this and any info about it you can provide would be great. Thanks beforehand for all of your responses.