Hi M.,
I've had a couple of experiences with my son that might be relevant.
First, my son was a very unhappy little toddler for a while there. The culprit turned out to have nothing to do with discipline or anything along those lines, though. Turns out, he had an undiagnosed sensitivity to dairy products, and that was resulting in clinical depression. I was VERY skeptical going into this, but when we took every last drop of milk/yogurt/cheese out of his diet, his mood turned around 180 degrees. If you look at him now, you'd think wow, this kid is not capable of being unhappy, ever. At 2, though, he was basically this teary little puddle, perpetually clinging to my leg.
Second, with my guy, punishment and negative incentives have almost never worked. We've tried the whole Love and Logic thing too, but any consequence I apply or threaten, he turns it right around on me. I threaten to confiscate his toys, he instantly threatens to confiscate my car keys. However, we've had great results with positive incentives. I'll say something like, "Wow, we're having a big problem with meltdowns around dinner choices. We really have to make some changes around here. How about this, if you can go for one whole week -- that's seven dinners -- without yelling even once, I will take you to the 99-cent store, and you can pick out any toy you want." This has worked amazingly, incredibly well. We get a week of trying incredibly hard, I'm out a dollar, and then a new (good) habit is ingrained. I do worry about basically bribing my son to be good, but the results are so good, and the alternative seems to just teach him to issue ultimatums all the time. So I say, keep it reasonable, make him really work for it, and then try bribing the little guy.
Finally, there was one period when my son did really well with negative consequences -- when for whatever reason he decided to have a weeklong temper tantrum at age 3. What finally worked (after I tried many things that didn't) was putting not him but his toys in time out. If he tantrumed, a Thomas train went up on the fridge, where he could see it but not reach it. When he shaped it up, the train came down. By day 2 or 3 of the trains-on-the-fridge routine, the whole tantrum at the drop of a hat thing had come to an end. This does NOT work with my son now (at age 6), but it did when he was younger, so you might give it a try.