Great minds think alike is a humorous expression to use when you find someone else doing or thinking the same exact thing you were.
I like it very much, because it is funny and also kind of flattering to the person you are talking to.
Imagine you are in your work and you propose picking up a screwdriver to mend the coffee machine. At the same exact moment, somebody appears with that. Ha! You say great minds think alike.
I wonder if Spanish has any similar idiom. Los genios pensamos igual is the direct translation, but does not sound that well.