Bumping up
Sounds like you have a good foundation already to me
A few little things my DH and I have employed that are working well with our 3 year old....
-I prefer timeouts in a corner instead of in his room because mine will just play with his toys. I had to go through a brief stage of putting him back and restarting the time repeatedly. I try to reserve time outs for the most serious behaviour - hitting, aggression - ongoing out and out defiance etc.
-I find my 3 year old gets very frustrated and loses control of his emotions very quickly. In this case I call it a calm down time - still in the corner but I give him his comfort stuffed animal and a pillow and I tell him to hit the pillow and hug his stuffy. Once calm we practice some deep breathing before he has to help me pick up/apologize etc. This has been working out actually really well. The focus is on his loss of control.
-In general for a 3 year old try to keep consequences, brief, relevant and have them carried out and over with very close to the incident. A 3 year old will have a shotty understanding of cause and effect and this is even worse if these is any distance between the event and the punishment. For example, in my experience taking away dinner dessert for not brushing your teeth in the morning would be nonsensical to a 3 year old IYKWIM?
-My DH and I read Dr. Harvey Karps "Happiest Toddler on the Block" and really liked the practical techniques given. For example our son responded well to the use of "hand checks" - a quick check mark on his hand with a marker or sticker on his hand for noticed good behaviour - it works well because its so immediate and the reminder stays there on his hand for you to point out latter on. There are lots of really easy to employ strategies in that book so I highly recommend it.
I think that one of the keys is keeping it positive. Dangle the carrot and not the stick so to speak. I know that this can be a monumental task but I do find our worse days are when I can't keep it light and positive. When I start coming down hard, lose my sense of humor and things go to the dark side, my kids are less cooperative, more sulky, more badly behaved and it just gets to be like a dark hole of a day.
Sorry, I hope I haven't rambled too much and that there is something of use in there.
Hopefully someone else will come along and add some more 