Unorth..
I guess any of us that have children have had similar scenarios happen....
My daughter was about 7 when she decided that she wanted to join some of her friends at school at cafeteria breakfast. (She ate breakfast before she left home.)We first got wind of this when the school called and told us how much money we owed for "charged" breakfast! So we told her no, we eat breakfast at home. Well, about a week later, we were in the video store getting movies for the weekend, when we ran into one of her little friends. They squealed and hugged and jumped around like they hadn't seen each other in years. When I commented on this, the little friend said, "Oh, no, I just saw her this morning AT BREAKFAST." The look on my daughter's face was PRICELESS.

First, we put all the weekend movies back. Second, she spent the weekend in her room. (That also meant no TV or computer)
That was not the last time she lied, but each time we consistently provided consequences, along with support and lots of talking about how there wasn't ANYTHING that she couldn't share with us, and how the consequences when we found out the lie would ALWAYS be worse than consequences for whatever it was she was lying ABOUT in the first place.
This approach has seemed to work well for us, as now, at 19, we have a very open relationship. She tells us all about her life and activities (even some things we would rather not know, but hey, WE wanted her to be honest, right?).

And we find that she has grown up making pretty good choices, and if there is a decision that we find questionable, we can all discuss it, and more often than not, she will take the advice of her parents, because she can look back and see that we haven't steered her wrong yet!