I'm sorry if this is redundant, though it doesn't sound like it from your update (I haven't had a chance to read all the responses). but I just wanted to say, it sounds to me like being punitive isn't working, and maybe you should re-think your whole strategy. I once read in a book something to the effect of:
when you want to push your child away, try bringing him in instead.
what it means in practice is, at those moments when you most want to put him into time out or yell or whatever, stop, and try and think about what's really going on with your kid, and if there's a way you can give him ~more~ of you instead of less. it sounds like he's acting out b/c he's trying to get your attention, so if you can really focus on giving him positive feedback for his positive behavior, it will help to re-direct his energies.
also, and this is really key, try carving out special one-on-one time just with him that he gets to direct, ie.: we have an hour (or ten minutes, it doesn't matter how long as long as it's as much as you can cobble together) together, honey, what do you want to do? play with trains? read books? go to the park? I'm all yours, we do whatever you want. (the only think you can't do is watch TV or go a movie or do something else that creates parallel play instead of the two of you actually interacting and playing together.)
you may find that the negative behaviors lose their power and so he may start to calm down. just ignore as much as you can. obviously biting and spitting need a response/guidance, but try not to give negative attention, and make up for it by giving as much positive attention as you can possibly muster. every single time you see him do anything positive, tell him you noticed and praise him: johnny, I see how nicely you shared your toy with your brother, that was great! johnny, I see how you really wanted to hit your brother because you were mad, and then you didn't, and I'm so proud of you for that. etc etc etc.
and when you're really mad, think about bringing him in instead of being punitive. think about being disappointed instead of angry. think about including him in strategies for correcting his behavior instead of meting out random punishments from on high (so to speak).