There was a message thread on the message board about the ideal spacing/layout for buttons on your arcade panels.  Michael B. has a curved button layout that has proven popular with his friends.  He was good enough to send me a to-scale scan of his layout for people who want to duplicate it.

I was in a hurry when drawing the buttons.  The cross-hairs are off center, and really only confuse you.  The dot is the actual center, where you should press the drill.  You may want to go in with a graphics editor and remove the cross-hairs to avoid confusion.  (saint's note - I did not modify the image, you'll have to do that yourself if you wish)  (This was really a preliminary template, I was going to do the finals in AutoCad, but realized it wasn't really necessary).
 
The circles are the actual size of an arcade button, not the 1 1/8" hole they are mounted in.
 
The joystick crosshairs are for the Happ Super Joystick.  If you're using a different joystick, check and see if the holes still line up.  The center hole should be good for all joysticks. :)  BTW:  I used the same 1 1/8" drill bit for the joystick center as I did the button holes.
 
Test this out on a scrap piece of particle first!!  Don't try it on your final control panel, dislike it, and blame me for ruining everything! :)