Ok, here are some of my PI clay designs I have been tinkering around with. I'm not sure which would be my favorite, since I like them all, so I leave this choice to you.

(for larger images, click on them)
Maya 2008:
I really like the concept of minimalistic mayan chips with the mayan numbers (using base 20) for the values. Since mayan numbers can't express fractions I omitted using those chip values.
If you have any suggestions for improvement, I'd be glad to hear them.
gnu:
This more modern design uses an alternative art GNU head and the ubuntu title font for the denominations with an edgespot gradient in the denoms and a gradient from black to the direction of the base color in the background. The gray chip could also be changed to a general purpose non-denom chip (EDIT: I just included this variation in gnu-a).
The gnu-a version places the new colors at the high and low end, so that the base set is intact and the new ones can be added later when they will become available.
gnu-b uses an alternative color progression for a different amount of typical playtime for the new colors, depending on your breakdown.
Personally I like gnu-a better because the stronger colors are in the middle.
to be continued ...