If you're looking for self defense, I'd look for a school that teaches you to
hurt people, rather than
beat people. Ask around your current training group first. You might already have someone who has something to offer, or at least get a reference. Failing that, call around, try some classes. Look for an instructor who's willing to tailor his instruction to your interests. Many of the techniques are going to be similar from school to school regardless of style. There's only so many ways to sit on a person and smash their head into the ground. Most of the differences will be in training method, philosophy, and finishing techniques.
Kajukenbo has a reputation for teaching grappling techniques with a striking, standing, and escaping philosophy. So does Krav Maga. Hapkido and JJJ schools are more likely to be taught as war arts. BJJ, Judo, and Western Wrestling are more likely to be taught as peace arts. But you can find TKD guys and kenpo guys teaching grappling classes these days too. You just have to look around.
I think the advice from
K831 was all accurate.
Find a school that teaches from a perspective that understands:
1.) You are easy to take down/throw, and rape happens from a guard position.
2.) as such, prevention of the above is first priority, ESCAPE from is second (not staying there trying to submit.)
3.) Class should take into account the importance of positioning to strike soft targets, draw/deploy and utilize both carried and improvised weapons while on the ground.
4.) Class should work on striking from the ground while in grappling range, but also, if you are downed and the opponent is standing
Any good instructor can teach you that, but not all instructors are interested in it. I don't teach sport grappling, many sport grapplers won't teach self defense. That doesn't mean their art won't work in a self defense situation, just that they don't train for that arena. We don't train for the ring.
Find an instructor you like. With no standard of quality in the martial arts community picking a style by name isn't very effective. A great style's name can be on the sign of some really awful schools. You want an instructor you can trust who knows what he's talking about, and the only way to find out if that's the case is to try some classes.
Good luck. I really enjoy ground fighting. It's a valuable skill, and a lot of fun to train in.
-Rob