Kidbell and Furball - wow, do I feel for you - ok, I had exactly the same thing with my dd when she was 2 ish (she is 7 now). She had the most epic tantrums ever - example - went to corner shop for stamps or whatever, and I decided to have some chocolate so she chose a bar and I chose a milky way, and she went completely off her head and in a Damian Omen type voice (possessed by devil in case you don't get the name) she screamed at me to put it back - I had to literally drag her out the shop as I couldn't lift her up and then somehow got her in the car, arms and legs flailing, screaming in this hideous devil voice - I couldn't do up the car seat as she was that hysterical. Eventually got home, put her in her room with the stair gate on the doorframe - she ram raided that with her pushalong horse which then got lobbed down the stairs along with the stairgate, toy beauty parlour and about 47 other large and heavy toys. I then ran into my room, slammed the door shut and phoned my mum, could hardly hear her advice on the phone as dd was ramraiding my door with some heavy implement and screaming wildly and damian-ishly. I was sobbing - completely distraught as this sort of tantrum happened very regularly for no reason. So here goes and please don't anyone go mad, because it flipping well worked. Take child outside, stand them there and tell them if they don't stop you are going to throw cold water on them. They will just carry on screaming, so then you follow it through and you throw or pour a jug of cold tap water over their head. I tell you this, the shock of it will absolutely stop them in their tracks. Clothes can be taken off and dry ones put on. Do it outside so you don't soak your house. Do it fast and mean it, and then tell them firmly that you will do it again if they don't behave. Tell them you are the Mum and you are in charge. They are NOT in charge. Then you turn and walk away so they don't see you start to cry because you will. I had to go in the kitchen and weep because her face was a picture, she just crumpled. Shock, pure and simple. And at the end of the day, she knew she was controlling the situation and deep down she didn't want to. She WANTED me to be in control but she didn't know how to stop herself. I had to do it twice in quick succession that day, I think the first jug made her scream even louder, but the second straight after totally silenced her. And afterwards, I took her back in, changed her clothes, gave her a little cuddle and explained that I couldn't let her behave that way because it was wrong and bad for us both. And she understood, and she NEVER had a tantrum again.
Now, there will be those of you out there who think this is absolutely disgraceful of me, but hey, it worked. Like my Mum said (and she raised 4 decent children), it is non violent, non aggressive, and it is a shock. I tried everything before trying this believe me, I tried ignoring, telling off, shouting, cajoling, shutting in bedroom, screaming back, rational discussion, bribery, and the odd smacked bottom. None of it worked. This did, and on the one occasion about a week later when she started to go into tantrum mode, I just said calmly to her "do you want the water jug?" and she stopped immediately. Simple. And completely effective. And she has been angelic ever since. Of course she carried on having strops, and mild paddies, which are normal, but never a major tantrum.
Sorry this is so long, but I feel for you two, and really hope you can bring yourself to do this, like I say, its not violent or aggressive. Just a shock. And its effective.