Search engine, for sure. Honestly, I don't know what I would do anymore without a world of information at my fingertips. Used to be that if you were wondering about something, whether it was the year Space Mountain opened, or who was that celebrity in that thing you saw five years ago, mostly you just shrugged your shoulders and forgot about it since it was kind of a hassle to find the information. I mean unless it was something general knowledge-y you could drag out the encyclopedia for (if you had them), you just remained blissfully ignorant. Now not knowing these things will bug the snot out of me if I don't Google it ASAP.
I don't use Facebook or Twitter so those don't matter to me.