I agree with you on ju-jitsu, it's very effective against one person at a time (hence great in MMA and any normal fighting competition) however, you have a real hard time going up against two. I recently heard of a technique called brawl-and-sprawl that is utilized by strikers to avoid getting taken down by wrestlers/grapplers. Here is a link to it, it would be hard to explain; http://www.youtube.com/watch?v=6KviIkLyHTQ
I also agree on the mixed styles, I plan to continue with Aikido and then go into Brazilian Ju-Jitsu and Muay Thai (always admired it greatly

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Vs two opponents is for Hollywood, not real life. You aren't gonna spin kick your way to victory vs two assailants. Real life fighting just doesn't work that way. If you have two people assailing you, your best bet is to flee. No kicks, no punches, no fancy moves will help you.
I was never a fan of Karate...it annoyed me that most of it had no real-world application to it (having said that, I was learning at 14, so it may just be that I hadn't got to the 'juicy' stuff). It also didn't really play to my strengths.
After a conversation with Exorince the other day, I signed up at the Bulldog gym, around 30 miles from where I am. I've started Kickboxing again, and taken up Muay Thai aswell. I was considering doing a 3rd course in Brazilian Jiu Jitsu, but if I'm doing the other two properly, I shouldn't need a ground game

It's the other way around. If you're doing BJJ properly you shouldn't need a stand up striking game. In all fairness, MMA fighters do not need to stand and strike except for ratings. There's tons of videos of BJJ fighters dominating strikers or stand up fighters because once the BJJ fighter closes the gap it's all over...and you're not gonna prevent that gap from closing if you yourself aren't a BJJ fighter. I'll link a few:
http://www.youtube.com/watch?v=VQXlg7DksvY
http://www.youtube.com/watch?v=mlleDPgmDVM
http://www.youtube.com/watch?v=0RawPYGzYOQ
http://www.youtube.com/watch?v=uEm-SVGlJrg
For anyone serious about self defense, grappling should be the foundation. That's including law enforcement and military who already train in BJJ. From that foundation you add striking, and Muay Thai is a great supplement because it's strikes from a clinch. The only problem is there has to be a BJJ/MMA academy near you. If you're serious I recommend staying away from karate, kung fu, taekwondo etc. because they have no real world application and their training does not focus on sparring which is essential.
Most real world fights end up with grappling, or wrestling on the ground.
That's a fact. All your fancy karate katas may as well be flushed down the toilet at that point. High school and college wrestlers are more skilled at self defense than most karate black belts.
(edit: some taekwondo techniques are effective when part of an overall training regimen that includes grappling, so what I said above is not totally correct. Just don't train it exclusively. It's not that useful an art by itself, unlike judo or jiu jitsu or sambo or even olympic wrestling.)