Significance of varieties prasadams in Vaishnavite Temple throughout India?

I would much appreciate if some one who can elaborate me the significance behind serving prasadams in temples and in particular Vaishnavite Temples. If one go to say, half a dozen Vaishnavite Temples, he/she will get different prasadams from each of those temples. Say for example in Tirupathi one will get LADDU but Sri Rangam Temple one will not get LADDU but a rice made of tamarind & spice. Who proposes these menus[Prasadam] and why? I don't want stupid answers since the question is of a religious one.