Another tip re flash (un-)predictability:
Sometimes it’s not the flash that is unpredictable; it is the review on your camera.
If your camera has a LCD brightness adjustment, set it to a constant value.
I was reminded of this the oterh day when I shot some shots with my 7D instead of the 1Ds. The 7D defaults to setting LCD brightness by itself. In these cases, when you take a shot and view it, you never know whether you are seeing a dark shot, say, or just a dark preview of a good shot.
In fact I found myself looking at shots twice, and once I’d see a dark shot, apparently underexposed; once, a bright shot, that looked fine.
I immediately realized what I was seeing, and I set the LCD brightness to “manual”, not “auto”. That problem was solved. I suggest you all do the same.
(And you really ought to use the histogram to judge your images, not the LCD, but you knew that already. Right?)