My son as diagnosed as having mild Aspergers when he was 7 and, honestly, having a name and something to research acted like a key. Once you understand what makes your child tick, you will be able to mitigate the situations that cause the outbursts, and life becomes SO much easier.
Children on the spectrum almost always have sensory issues, and the sooner you can tune into your son's the easier life will be. My son can't handle noise, it stresses him out, and stress results in outbursts. He also NEEDS touch, constant physical sensory input, so chewing on a shirt or a straw or a carrot calms him down and helps him focus. However, these things are unique to each child and you may find that your child calms to music, instead of stresses, or calms to something visual, like staring at a brick wall (one adult at an Asperger's forum I frequent described how he used to see patterns in this one brick wall near his grandparent's house, and could stare at it for hours re-drawing patterns in his mind. He posted pictures on walls outlining the types of designs he saw. It was a fascinating look into a mind that is very different from mine).
Think about some of the things your son is drawn to do that you may have been prohibiting. For my son, one such behavior is pacing. It turns out it is a very common pattern, for Aspie's to pace. My son literally walks from one side of the room to the other, climbing up on the furniture, banging the wall, and then reversing. For years, we tried to stop it, but after reading on the Asperger's forum how important this can be to self-calming and focus, we decided to just let him. And, well, it WORKS for him. Other Aspies talk about loving to swing, or jumping on a trampoline; they seem to all have some physical movement that helps them focus their mind and calm themselves. See if you can spot what your son is drawn to, and if he doesn't have anything in particular, see if you can help him find something acceptable to you that will fulfill this function.
Asperger's comes with gifts and burdens. Once you understand how to mitigate the burdens, the gifts start to shine more clearly. My son is an inventor, he has the most amazing imagination. He is a fabulous story teller and actor, gifted at math and science, and blew everyone away at my father's funeral by bravely and beautifully reading from the Bible in front of the church. But he struggles to write, can't really tie a shoe, can't remember basic hygiene, and is afraid to ride a bike. So it goes, with a child like this. Gifts, and burdens.
Hopefully you are in a public school that understands the condition and will deal with it in a positive way. If not, MOVE SCHOOLS. By and large, children with Asperger's love to learn, yet most have very negative school experiences because they have trouble fitting in with the patterns and social settings of most schools. My son, however, has had a FABULOUS elementary school experience, so I KNOW it is POSSIBLE, and urge you not to settle for misery. Among other things, misery leads to behavior issues. Happiness mitigates them. Your life will be MUCH easier with a happy child.
Read all you can to understand your child. Advocate for him at school. Help him navigate friendships. If all goes well, you will find yourself with an amazing child that shows little "bad" behavior.
As for the Asperger's forum I like to read, I'll share the name with you, but caution you about dipping your foot in there. The forum is Aspies for Freedom, and a lot of the adults hold quite a bit of anger towards the NT (nuerotypical) world (including, often, their own parents), plus as is the nature of Aspergers they tend to be very blunt. But I have learned so much from them, it just takes a thick skin. I go there respectful, looking for insight, and that helps me be accepted.
We have considered the special diet some other posters mentioned, but it is very difficult to follow, and only about a third of those who try it find improvement. One father at the Asperger's forum told me that what he has done for himself and his boys (they all have Aspergers) is to take out only the glutten, not the casiene, and that it has worked well for them. Basically, it does seem that those on the spectrum have more digestion issues than those who are not, and the special diet is this giant slam at fixing it. If you think you can follow it, it certainly cannot hurt, and I would much prefer trying that before agreeing to medication of any sort. But, first and foremost, you have to understand that your child has different needs than other children, and as long as you honor those, he should be fine.
Good luck!
ADDED 01-31-08:
I want to add that Sherry, above, made some excellent points. The rigidity she mentioned is very important for a parent to understand. It isn't about being stubborn, it is about a true inability to absorb something different. A different routine, or a different opinion. Issuing consequences in these situations will only frustrate the both of you, and make things worse. Instead, you have to try to bring the concept to their form, to something they can understand and absorb. And it's also to good to have a conversation about flexibility, how you know it is difficult for them, but that life is going to require it. All of this will take time, but please be patient when you run into those situations. Your child CAN overcome it when most necessary, but it will take patient work, and you definitely need to pick your battles.