What is a Normal Tip to Give a Server if Everything Went Well?

Yesterday as well as being New Years day it was my wife's birthday. We had a party for here at local seafood joint in Lewiston-Auburn. It was a reservation for 17 people. We had a blast, the food was awesome, the service was just as good. The server basically forwent asking everyone for dessert as we brought a cake. It was an amazing job done by her and the rest of the staff.

I just want to thank our server, whose name I never got in the craziness. I know it's hard to keep a party that large satisfied for two hours. She did an excellent job. I think I tipped adequately at about 25%, but what is the tipping norm? I normally hit about 18% to 20% on a normal sit down meal (less at a buffet) but where we were there a long time compared to a normal table turnover and her getting as far as I know all of the orders right, what is the right amount of gratuity.

I feel for servers in general, and know that a tip for them is like a commission in sales and more often then not, they get the brunt of the unhappy patron even if it wasn't their fault or accident.

Over all a job well done.