UnderGround Forum >> I wanna take a TMA. Whats fun?

Sajite - Try some filipino stuff

Xspur - The filipino arts are great as mentioned, and they flow from hand to hand, close range and medium range weapons very effectively.
For a martial art that's abit easier to find than say, Krav Maga, (depending on where you live.) that's geared more towards practical self defense, Kenpo is a fun and disciplined style. You will find multiple variations, so like a BJJ school, just research the lineage. Most will derive from William Chow, Edd Parker, or Bruce Juchnik. All credit James M. Mitose as founding father of Kenpo.
If you want to have fun, learn some really flashy kicks, and get a great workout every practice, Taekwondo is right up that ally. The focus on kids you see is geared towards marketing, don't let it fool you. There are also different versions and "philosophies" among the world of Taekwondo. There are more competition orientated schools and more traditional schools. The good thing is they almost always let you watch classes for free. So do a tour and see what's out there!
As far as weapons go, my favorite are the Filipino stick and knife stuff. But there are allot of styles that teach swords, which although my training was brief, it was really fun. That was at an aiki jitsu school.
I think the first thing you need to consider when choosing a "style" is what best suites your personality and body style. There are more Power & Strength-based technique styles like Boxing, Kickboxing, Karate, and Tae Kwan Do. And there are styles that almost exclusively use the opponent's own energy/balance against them like Tai Chi Chuan, Aikido, Hapkido and Aiki Jiu Jitsu.
Personally I found Kenpo to be the best blend of the two, but to be honest, I haven't tried everything.
Call around, interview some instructors, try some free/discounted first classes and see what's in your area.
A couple tips though, be wary of schools that require a "contract". I'm not saying that they are all bad, and if it's just an option to save some bucks it's usually harmless. But if it's a requirement, I'd shy away. This is an aggressive and effective marketing tool used to guarantee revenue for the school, but from my experience when a school focuses on buisness more that art, they have lost the essence of what is Traditional Martial Arts.