I second the "read Alfie Kohn" suggestion. My DD is, fortunately, pretty easy-going and doesn't really do the tantrum thing, nor is she ever really what you could call defiant or disobedient - but then again, she's never been punished, made to feel shame about things she's done, or put in a time-out. Without an identical twin being raised differently elsewhere, it's hard to say what's the cause and what's the effect, kwim?
I try to treat DD with respect and understand that her needs and desires are no less valid than mine just because they come from a 3-year-old instead of a 36-year-old. I can't envision a situation in which I *would* put her in a time-out - if she's upset and unreasonable, she needs cuddles and comfort, not sitting alone. If she's angry, there's probably a good reason, and she needs to have the opportunity to tell me exactly why. If she's doing something she's not supposed to, and keeps doing it even if there's a good reason not to, then there's something else going on and it behooves me to figure out what it is, which is very much more difficult if she's pissed of at that AND pissed off that she's been told to sit in a corner or whatever. It's not very conducive to eliciting cooperation.
So, I've never been even tempted to use a time-out. I'm a pretty flexible person, and I think that helps. One thing that I've noticed leads to tantrums and time-outs in other parent-child dyads is that parents say "no" or "we have to do X" without really thinking about it, then feel for some reason that they have to stick with what they said when the child objects - like it's somehow damaging or wrong for a parent to correct him/herself or accede to a child's wishes, even if there is no reason not to. I think parents sometimes think that if they can be swayed by a child's argument sometimes, they will be taken advantage of, or the child will want to always have her way, or they will "lose the upper hand."
As to the latter, I don't believe in having an "upper hand" to start with - children are partners in family life, not subservients. As to the former points, I think children are more likely to be accepting of decisions when they can trust that you don't enforce something they're not happy with unless you've got a darned good reason. I have never used the phrase "Because I said so" - I've always provided an explanation, and if I can't come up with a good one, then obviously DD is quite right to question me and object. If I can, it helps if some of the time she can understand that reason, but even if she can't understand the reasoning, I think she knows bull**** when she hears it, so I don't try to make up a grown-up-ish excuse.
Anyway, this is a bit of a rambling response. I know I am blessed to have a child who has always been largely agreeable and reasonable beyond her years, but I also think that the parenting style that I (and my DH) employ has worked with her nature and enhanced it. I also know that all kids are different, and it's entirely possible that I'm talking out of my backside if I think that my approach could be generalized