Lucy is one of my favorites!!
Another vote for the chocolate factory ep - which is also the one where Ricky and Fred decide to make arroz con pollo for dinner... they make about 4 lbs of rice (which of course expands to fill most of the kitchen), and the pressure cooker with the chicken inside explodes!!
What always impressed me about that show, is that it used only clean humor... no crude sexual jokes or anything... and that it's still funny today, nearly 50 years later. (Even though I could never be a housewife
)