As there seem to be a lot of behaviour threads just thought I would add the latest piece of advice that I've been given. I attended a really good parenting course recently which reinforced alot of stuff but I camne away with one really good tactic which really works with my DD.
Don't get involved in her arguement. So when I've asked her to do something eg. put shoes on don't get involved with her resaons not to do it just reinforce what I have asked her to do, using phrases like I hear what you're saying but I would still like you to put your shoes on etc.
Another tip was give them warning when things are going to happen. eg. You have 5 minutes left to play before we are going home - really works with my DD she is much more accepting of leaving places or going somewhere.