How to Discipline a Toddler: What is age appropriate?

We are now getting to the phase with Sam where she is acting like a toddler. A terrible-twos-type-toddler. I know she understands the meaning of "no",yet there are many times when I will tell her to stop doing something and she will just stare at me and continue to do it, blatantly defying me. And other times, I have to take something away from her, and she will throw a full-on tantrum. It usually doesn't last long, and she'll finish with a smile and sweetly say "hi" (which is just adorable!), but still. These tantrums are getting more and more frequent. What is appropriate to do for a toddler at this age? Should I put her in her room? Should I give her a time-out? Should I just wait it out?

It's so amazing to see how human nature just kicks in at such a young age. Today I could hear her pushing buttons on the printer. When I walked in the room she quickly stepped away, put her hands up by her shoulders and said (as best as she can) "I didn't do it!" I didn't teach her that one, I swear!

Sometimes it's hard to be consistent with rules because she can just be so cute and charming, but I also don't want her to grow up to be a bad kid. How do you handle situations like these? How do you enforce the rules with a 15-month old? I don't know how much she understands, and what will really make her understand that Mommy and Daddy are in charge and no means no.

What are your discipline tips for toddlers?