Obviously 2+2, but I think that goes without saying. Another one is Wikipedia. I'll start out reading an article about, say, the atomic bombings of Hiroshima and Nagasaki, and 8 clicks and an hour later, I'm reading about a cannibalistic tribe of leopard men waylaying travelers with sharp claw-like weapons in the form of leopards' claws and teeth, wondering where the hell the last hour went.
(Atomic bombings of Hiroshima and Nagasaki --> Potsdam Declaration --> Winston Churchill --> Second Boer War --> South Africa --> Kruger National Park --> Leopards -->
Leopard Society)