I was just at a 70th birthday party at Maggiano's. They label your party room with the party name which made us feel special. I have to say it was very nice, even though I'm not a huge fan of their food. It might be pricey, though.
We had a bday part recently in one of the Hudson Grille party rooms. The food is a little above average bar food, but the atmosphere is good, especially in their party room. It would be cheaper than Maggiano's. The Sandy Springs or Midtown might work for you. http://www.metrocafes.com/hudsongrill...