Plugin/Widget for Contact Forms?

Could someone recommend a free Plugin/Widget for building forms into “Pages” or “Posts”?

I’d like to have something that lets me insert a really basic Contact form onto Posts or Pages, but allow me to configure that Form and give it some sort of unique identifier for whenever it is “Submitted” (e-mailed into an e-mail box that I can configure) that will differentiate it from other of the same Contact form that will be on other Posts or Pages of the website.