Yelp!, Urbanspoon, and Munch use GPS to find nearby restaurants. Urbanspoon, the most restaurant-specific of the three, allows you to search them by neighborhood, cuisine, or price.
Restaurant Nutrition stores the calorie information from various fast-food chains. Kind of useless now that calorie postings are de rigueur.
Meal Splitter, TipCalc, ACTGratuity, and BigTipper calculate tips and make it easier to split bills among friends. Nothing your old PalmPilot couldnt do.
Limbo, Loopt, and Whrrl allow you to see where your friends are, so you can join them at a certain bar or restaurant.
And lets not forget that if you want to get recommendations from good ol New York, via text, theres always our mobile restaurant and bar listings. Now if they could just find a way to make your phone double as a microwave