The Vaad of Fairfield County supervises two caterers-Esti's and Simcha. Contact info is at http://www.vaadct.org/services.html. If you want dairy or fish you can also get from Sweet On You Cafe at the JCC in Stamford.
Westchester options: Supersol in Scarsdale, New Roc Glatt in New Rochelle. Eden Wok or Grill Point in New Rochelle could also do something nice.