This friendly little diner is set up in the back corner of the 42 Boston Post East shopping center and most of the cars in the lot are for this joint. There is an ever-changing specials board and endless pots of black tar coffee here. Pancakes and steak and eggs are a perpetual favorite here and Sunny Side seems to be exclusively patronized by Marlborough's retired community. There are several tall bar stools but most sit at the slick wooden booths.