C.,
This seems so much more than terrible twos, we expereinced the same kind of behavior from our daughter. I would suggest that you consult a Developmental Pediatrician. You can find them at your nearest children's hospital. This is not your regular pediatrician, a Developmental Pediatrician is a specialist and if it is just his strong will, you have lost nothing by knowing that, and you may be taking the first step in getting him the help that he will need now, and later.
In the mean time, stop trying to reason with him. Make a plan every time you go some where, and tell him what will happen if he has a tantrum. Since he does not seem to be able to hear you once it starts, don't try to negotiate with him, just follow through with removing him as quickly as possible, and leave him in a safe place until he is done.
Tell him what you want him to do not what to stop doing. This is much harder than it sounds, but in general, this will be very helpful at his developmental stage. Generally speaking, success breeds success, and the more you can set him up for it, the better. Keep a log for the time of day, the trigger, and how he behaves so that you can really describe what is going on to a professional. You may be surprised by the pattern once you see it on paper.
Last, when you have a child with these kinds of extreem outbursts it is natural to have a hard time liking them, so don't beat yourself up about how you feel. You may need to seek out care for yourself, espcially if this turns out to a symptom of a more difficult diagnosis.
M.