I have an angry son, older than yours, and we've tried everything we can (but haven't given up on him), so I can relate and send hugs out to you.
The doctor who prescribes your son's meds -- is he/she aware of everything you've described? Is the doctor a psychiatrist? Maybe you need to start there, as far as finding a psychiatrist, who will work well with your son regarding ADHD and ruling out any other diagnostic possibilities.
Be consistent (that is so hard to do sometimes/sometimes it seems it would be easier to just give in and give up). Some kids will test to the limit and beyond. At home, providing structure and basic rules that he can grasp will help, as you may already know. Recognizing and rewarding accomplishments should help, too. Another point -- at least it is so in my case -- I have to remind myself that my son is not at the level of maturity that I would "expect" for his age group. I end up adjusting my expectations to what I would for someone a few years younger.
Is the school on board? How is he doing there? What accommodations are in place?
Keep us posted. I hope I have been helpful. Best wishes. 
I agree with the maturity comment, they say they around roughly 2 years below their age socially and probably emotionally.
Do you think that there could be another diagnosis that could be involved, any depression, anxiety?
It is very common for the adhd'ers to have more than just adhd going on.
I would look into another possible diagnosis and his meds. They may be too low, too high or just the wrong ones for him, especially if there is something else in addition to his adhd.
hang in there and best wishes!!
trevman,
My ds is the same age and we went through the exact same thing. I am a fairly consistent person and stick to the routine & rules that I set. I have always had structure and provide him with little rewards for the good things. I have learned that once you punish for the bad it becomes a viscous cyle and only ignites him. I found that if I praise the little things he tends to make better choices as he likes to be praised and get little rewards. However we hit a road block and despite all of this he emotionally spiraled out of control. Sadly it got so bad that he refused to shower, take care of himself, was afraid if I was out of the room and eventually wanted to die and at points was begging me to kill him. I can't even begin to tell you how heart breaking this was. I made an emergency appt with his dr and they came back with a dx of anxiety. We have been treating it and he has improved immensely. However I am noticing a slight decline and he is being a little moody this past week. I am going to watch/journal over the next week to see what goes on. I really suggest meeting with your dr to see if it could be anxiety.
Wishing you the best with your little guy keep us posted!
My son was angry too and it was getting increasingly worse as the months and weeks went on last year. At that point he was only on tenex and we tried all alternative therapies to help with the ADHD. However, since nothing was really helping I believe he developed ODD (oppositional defiant disorder), and as I mentioned it before, it was getting worse each day. His behavior was erratic - 30 times a day telling me loved me which sounds sweet but it wasn't right. His reactions, too, were way over the top - screaming fits, extreme anger, violent behavior all because of normal requests made by me.