All I can say is you aren't the only one going through this. My son is nearly 3 and he is a little monster at the moment, specially if he hasn't had his nap. All the things he knows he can't play with, he has started to play with, including jumping on furniture, the bed and playing with powerpoints. I am constantly telling him "NO" but he just seems to smile and goes back to doing it. It is like he is testing me, specially considering I am 34 weeks pregnant and can't move fast. I too put him in his room for time out, and it works for about 10 mins then he goes back to it, so he is back in his room again. And then there is being the monster in town, if he doesn't get his way he throws the biggest tantrum and sits on the floor and doesn't move. No matter what you do, he just looks at you. I am hoping it is just a stage and he will eventually grow out of it, soon I am hoping. I hate having to keep telling him of or giving him the odd smack or giving him time out. He is a little angel when he gets his own way or he is in a good mood. It is just lately he is pushing my limits, I sometimes I think it is because he knows mum can't move as quick as she use to, but don't know, it has only been this bad since I fell pregnant. It is like, you get to the end of the day and can't wait for hubby to get home so you can sit down and relax and let dad deal with it!
Sorry I can't really help with ideas on what to do, but just letting you know, you aren't the only one giong through this.