OK, given that information, I'd go for a 580EX II. It is a better flash than your 430 for several reasons. It has a reflector panel built-in. It swivels 180 degrees in BOTH directions; your 430 only does that one way, and 90 the other. The 580EX II is more powerful, which comes in handy when bouncing flash or using diffusers. It can also control 3 groups of slaves. The ST-E2 can only do 2 groups. BTW, your 7D can control 3 groups all by itself.
I understand your point about the 18-200 filling your needs. I got sucked into the L-glass G.A.S. problem a few years ago. I eventually sold L-primes and got a Sigma zoom. I am happy with it. I use mostly mid-range glass, and it outperforms my abilities.
Sorry if I seemed a little blunt in my last post didn't mean for it to come off that way.
Also I wouldn't mind L Glass eventually but only certain lenses from that range interest me. And thanks for the advice again sorry if I was a bit blunt.