I decided to try a "physically correct" simulation of a mirror in Cycles nodes: two parallel planes, the back one with a fully reflective shader like this

and the front one with a glass shader that has a very faint green tint, almost white. I think the result looks quite nice:

One could also use a very shallow glass box with a separate reflective material on the back. I think this method could also be useful for simulating various forms of blemishes and damage that happens in real mirrors, but haven't tried much in that direction yet. I think it's important not to have a perfect reflection, or the mirror will end up looking like a portal into a parallel dimension.

-- I'm not mad at you, just Westphalian.