OK so call me over ambitious, but after some inspiration from darthpaul's ridiculously cool 
automated cabinet, I've decided I want a piece of that pie too.

Here comes the rationale on the controls I've chosen for the 3 sides.  I'm aiming for all joysticks to be leaf-switch ball-tops, and all controls to be LED illuminated (if I can).  Comments/feedback/criticisms welcome, of course...
SIDE 1 - Single Player Dedicated
From left to right:
 - 2-way vertical joystick (for Defender) along with dedicated reverse button
 - 2-way horizontal joystick (for galaxians, galaga, etc)
 - 4-way joystick
 - 8-way joystick
 - 8 buttons - should give me enough for most games I can throw at it... the extra buttons will also come in handy for C64 emulation (e.g. buttons for Spacebar, Run-Stop, arrow keys, Return etc)
SIDE 2 - Two Player + Trackball
From left to right:
 - Player 1 controls (8-way leaf, 6 buttons)
 - Trackball (will use this also for Star Wars, and probably some ScummVM games)
 - Player 2 controls (8-way leaf, 6 buttons)
This will be my robotron panel! 
SIDE 3 - Spinner/Various
 - The top half of this panel is for 2-player spinner games such as Blasteroids and Two Tigers, plus with mini-racer wheel can be used for Super Sprint etc.
 - The spinner in the middle would be for dedicated arkanoid or various single player driving games (TT2 w/mini-racer wheel)
 - The bottom 5 buttons are for dedicated asteroids 

 - I can also play Tempest on this panel 
 Can't play Tron. Can't play QBert.  Most of the other games I care about I can play though.  I don't think I've missed anything out but if something is glaringly obvious I'll be happy to hear it.
It's a bit snug under the panels, but all the controls fit and I have an idea or two on how to rotate it (thinking: stepper motor again). Keeping the CP securely in place after rotation is another concern... electromagnets maybe... needs more thought.
I haven't specifically allowed space for an interface such as IPac yet either... and I'm sure something else is going to come and bite me in the ass too.