Treat your teen and a few of his or her friends to a pop or rock music concert.
As the parent, you, of course, will sit a few rows back to keep an eye on things and make sure that the kids (and, perhaps, every one around them) are behaving themselves.
Purchase concert souvenirs as party favors for the kids.
Go to a restaurant before or after the concert for a meal and birthday cake.
If you have the budget, consider renting a limo to pick the party (and parent) up and drop them off safe and sound!