Counter Service meals are any of those that you walk up to the counter, place your order and wait to get your meal on a tray basically. Places like Cosmic Ray's or Pecos Bill's in MK, Electric Umbrella or Sunshine Seasons at EPCOT, that sort of thing.
On the DP, a CS meal for an adult means either an entree and side or a combo meal (think double cheeseburger and fries), a dessert and a drink + tax. For the kids, they need to order from the kids menu, which is generally the meal (like nuggets) with 2 sides (grapes, applesauce), a dessert (which I have heard have been expanded to include pudding or a cookie) and a drink + tax.
Many people feel that Sunshine Seasons offers a great variety of items that are available for CS. If you're anywhere near Coronado Springs, their CS restaurant is much like a table service with the variety available.
We're big fans of Columbia Harbor House, for the fish and chicken. Also, there are a few places where there are no "kids" meals so the kids can order the same as the adults (Casey's at MK, Toy Story Pizza Planet at MGM).
Hope this helps.