Honestly, you should tip at almost every restaurant. Anywhere from Starbucks, to Golden Corral, to Applebees or Red Lobster. The people in the food industry spend their whole day of work serving other people. Even if it's just catering to everyone's parched throats by bringing them water (try doing that for 8 hours straight!). Tip at Subway, Quiznos, and Port of Subs as well. Also, tip at any sort of coffee shop. The only place I wouldn't tip would be fast food chains like McDonald's or Wendy's or Jack in the Box, etc. Leave the money in an orderly pile in the middle of the table.
***Waiters and Waitresses usually only make $4.00 at the most per hour. They rely mostly on tips for their income. So at restaurants where you have a server, ALWAYS tip at least 15%; more if you have a large party!