I had a quick read through all the new posts to this thread. I'm pretty much in agreement with what's been written about flash photography, but I did note that the advice did seem to be quite strongly polarised towards the type of shooting that that poster did - which of course doesn't necessarily equate well with the type of shooting that the OP may wish to do (and thus the advice may not be particularly relevant).
With regards to flash for general photography (which I'd class your requirements as) it's definitely an asset. It's one of those things where you don't have to use it it you don't need it -- but it's invaluable for situations when you DO need it. A lot of people don't use it because they don't understand it -- and their results suffer because of it. In photography, many will say "you can still get good results without {insert name of feature or accessory here} - which may well be true - but don't forget that on many occasions getting a picture isn't sufficient if it's not the picture that you want. Case in point - someone may say "flashes aren't for me - I prefer to only shoot with natural light"; they may well get natural light results that work for them, but they're going to be up the creak without a paddle when they need to take that cute photo of a baby grand-child who's fallen asleep in grandma's arms late at night. Having to say "sorry - although I'm a photographer, I'm only a natural light photographer" just doesn't cut it in those situations. As a (some days) professional photographer I feel I need to be equipped to take the image the client wants -- not just a "cool photo" that fits within narrow limitations of restrictive gear. That probably won't apply to you to that degree, but I do feel that every photographer needs a base skill set before they get more specialised into macro, birds, landscape etc - and thus they really need to have some basic tools for that general photography. And in that basic toolbox I'd definitely include a flash, tripod, and remote release.
In terms of flashes, a 430EX II is a LOT better than nothing; I'd definitely buy that in preference to cheaper off-brand units (for a number of reasons). Having said that, if you're already feeling a strong pull towards high-end amateur / professional level location portraiture then I'd suggest that one starts saving for something more capable like a 600EX-RT (I'm up to 6 of the little blighters now). It is a significant investment - but it does make life a LOT easier having a quality and reliable portable light source; yes, often there are potentially effective work-arounds, but often they're hard work at a time when you're already busy enough wrestling alligators on a shoot. For location shooting, the best "bang for my bucks" came from a simple ETTL flash firing into a shoot-through umbrella that was mounted on a pole held by a VAL (Voice-Activated Light-stand) (usually a daughter or models boyfriend).
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