What Should I Wear To A Birthday Party (Male)?

I'm attending my friend's 21st birthday party. We are going to a somewhat fancy restaurant and then bar. Usually when I go out I wear jeans, a button up and casual/athletic shoes (addidas). My friend would like us to dress up a bit. I don't want to do a full suit or look too overdressed or stuck up. Any suggestions for a middle ground between what I usually wear and a suit?