I am in the same boat with those that say it should be a simple, generic design. I think a lot of the designs are great, but to appeal to the masses, I think it needs to be something that has style but is very basic...so far, these are my favorites:
The one on the end with the actual number
with a darker inlay background and maybe a spade shape around the denoms
Maybe with the background muted a little bit more so the denoms stand out better
I also like the idea of what was done here by a CT member
Great job so far everyone!
