Aetna, Merck, Pfizer are stocks to watch Tuesday By: MarketWatch July 29, 2014 at 05:30 AM EDT Herbalife posts disappointing earnings; Aetna, Merck, Pfizer, Twitter report Tuesday. Read More >> Related Stocks: AFLAC Aetna American Express Amgen Darden Restaurants El Pollo Loco Express Scripts Holding Herbalife Ltd Marriott International Merck & Co Pfizer Reynolds American Siriusxm Holdings Inc Twitter, Inc. United Parcel Service