The power of AskMe for identification.
This AskMe looking to identify a weird receptacle really blew me away. Being able to make that identification with supporting images is one of my favourite things I've ever done here. And I'm in awe every time someone answers a what is this book from a vague recollection of it (usually 50% or more wrong). Especially when it isn't "All Summer in a Day" by Ray Bradbury. iconomy identifying the spider game is my favourite in that vein.