we do similar to LaTrucha. If dd hits deliberately (which she does do, particularly when I am trying to do something and not paying her 100% attention) I tell her it really hurt me and that it is not nice. I say this whilst bending down to her level and I do use a firm voice.
I ask her to apologise. some of the time she will, but most of the time she won't and will shout at me "I NOT SAY SORRY. I NOT SORRY". I then take her by her arm and move her out of whichever room I am in, over the "line" into the next room/hallway. I tell her she must stay there until she can say sorry. I stand right near her loking sad (and i move her back over the line if she tries to get past me).
Eventually she will say sorry and we will cuddle and then play together.
My theory is that I cannot just leave it, because if I don't discipline now, at what stage will I start? And if I ignore it, or just look "hurt" she would not care and would go on playing with her toys. This way, the consequence is that she has to see me feeling sad, and do something about it before she can do something she wants to.
I don't think it the perfect method, but she is getting better, often she now tells me she wants to hit me, or will apologise immediately and then not do it again. There are only a few ocasions where she is in such a rage that she can't help herself.
Oh and I also tell her that she can hit the sofa, a cushion, the floor etc rather than mummy if she is cross.
I think dd is a similar age to your son if I remember correctly (26months?) and is a similar temperament