Hi Raelene,
I know the feeling of dread when it comes to medication. It is difficult to place your child on it. We ultimately did but went the natural route when they recommended MORE medication.
Try a book called the Nutrition Solution. It is quite informative. Though, I have to admit if you followed it completely it would be a very difficult task. We picked what we thought most important (including fish oil...for the omegas). Go get a lot of books on natural/behavioral treaments.
We also did several months worth of Japanese Medicine therapy. That included acupuncture and herbs. My 11 year old tolerated the VERY tiny needles well, but I am not sure how well your little one would. We and his teachers felt it made a big difference in his behavior (he is also heavy on the HD part).
Is his psycologist doing behavior modification? As far as the ODD.... Our difficult child developed that last fall for a brief stint. No fun is it? His therpaist suggested to us that it is possibly a compensatory mechanism in response to years of us being on his case ALL of the time. We backed way off and it was amazing. I know you can't back off on everything, but we were in the habit of pouncing on him for just about every movement out of frustration. The more ODD he got the more we got on him. Just a thought. I know every case is different.
Good Luck. Let us know how it is going.