First of all anyone that does not tip even if they feel they got poor service is a fucking loser that should be eating at a fast food restaurants. Even if the service is poor you should at least leave 10%, don't forget that food was ordered for you, cooked for you, served to you at your table and cleaned up after you left, that is what the tip is for!!!
Secondly, my standard tip is 20%, however it can go up considerably if I get really good service. I have tipped as high as 50%, and it never hurts if its a hot (female) server that flirts with me.