I recently discovered this site called "Peter Answers" which is a great site to use to prank others. I've gotten great success when using it on my friends. You'd think that after awhile they'll catch on as to how it's done, but they really NEVER do. The secret never seems to occur to them.
Instructions on how to use the site can't be found on the site itself. Here's a guide to follow to learn how to trick your friends into believing that a website can read their minds.
Awesome Prank: Guide to Using "Peter Answers"
Happy prank-ing! :D