The jack o'lantern mushroom (Omphalotus olearius) is a poisonous orange mushroom that glows in the dark. We've found it twice in the last two weeks -- perfect for the lead up to Halloween!
But the truly cool thing about these mushrooms is that the gills glow in the dark. You need absolute darkness to see it, and they need to be in their prime (one source recommends wrapping them in moist paper towels to bring home).
Just don't go trick-or-treating on these beauties. They may look and smell great, but they'll make you really, really sick.
In the wild: We've found these mushrooms twice in Rock Creek Park (once on Oregon Avenue and once by Boundary Bridge), and also in Scott's Run.