Sounds like you guys are doing it tough.
Have you thought about a 'time out' technique? Some of my friends are beginning to use this already with their little ones who are about 18mo like my DD. They offer a warning, then if the behaviour continues they place their child in their cot for 1-2 minutes, and leave the room. Apparently they've had some success already.
I agree with the theory behind the 'time out' technique, that they are in a safe place, and they are being deprived of attention (for a very short time), which is usually the main motivation behind difficult behaviour.
Having said that, I've not actually tried it yet myself, so I can't offer you any personal stories.
Probably above all else though, we need to offer our little ones consistency. I have been trying to adjust my reactions to DD's behaviour to be more consistent of late, as sometimes I am more lenient than others. This is too confusing for her, so I'm trying to rectify this. I don't know if this is an issue for you too?