I would never have thought that Ollie's bestest friend would be an inanimate object, but it is.
He loves my humidifier. The noise it makes when it drops more water from the tank into the tray, coupled with the bubbles, just fascinates him. He lays next to it in our bedroom like he's guarding it. And if he happens to bump it and make it gurgle he whips around and stares at it like it's come alive.
Once a week, I completely empty the tank and let the various parts dry out. When the tank is refilled and placed back on the tray for the first time, the thing burbles like mad. Ollie is particularly entranced then. This video gives you some idea. :)