Has evolution stopped?

Had a thought this morning. Has the process of human evolution simply stopped? Have we reached perfection? Why are there no evolved examples of humans with, say, a third or fourth arm? There have been many, many times I thought having a third arm would come in very handy. How about a third eye, maybe in the back of the head? Or a pair back there, for stereoscopic vision with depth perception? How about a hearing membrane on the back of a hand, to make it easier and cleaner to hear somebody trying to whisper something to me? It just seems that, over the entire course of human evolutionary history, there should be some examples of at least one handy adaptation or another carried down via reproduction (the normal kind).