The point isn't really what numbers you are supposed to repeat to yourself, but rather to "zero out" or "reset" your mind and thoughts. I have used a "Swedish version" for this, and 9 out of ten really say the same thing afterwards. You should really do it live though, doesn't work the same when you read it.
Naturally, the result varies from place to place, depending on culture and the area you live or was brought up in.
Tell them ahead of time that after they will be asked to name 2 things.
Repeat the number 6 (or any other number from 1 to 9), each time adding a six to the total number --> 6, 66, 666, 6666, 66.666, 666.666 (six, sixty-six, six-hundred-and-sixty-six etc.).
Let them do it until reach about a billion or so, then ask them for a colour and a tool (write these down on a piece of paper ahead of time for the punchline).
Over here, 9 out of ten say Blue and Hammer. It would be interesting to see if the result varies from region to region (I'm not a psychology major or anything, just curious).
Post your results here or PM me, I bet my GeForce 2GTS that the results will be similar in areas respectively.
/B