Birthday Party in NYC
You might want to consider Bocca, on 19th St., b/t Park Av. S. & B'way. Very good Italian food, friendly service, and contemporary decor that has a hip feel. We were there on a rather quiet Friday night in June not long after it first opened, but since then, reports on this board indicate that when it's busy, it's very lively.
Barbounia, on the corner of Park Av. S. & 20th St., serves pretty good Greek food -- mezzes are great for group sharing -- in a huge, attractive space that has a bit of elegance about it and is always very lively.