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Oophaga pumilio
Here's a good web page showing some of pumillo's variability: http://jeb.biologists.org/cgi/content/fu...
The thing about pumillo is that they are extremely varibale in color and pattern, so it's a good guess. It's also hard to go by the available images in book and on the web because they usually use the most spectacular examples of the species, and not the dull ones.
That's the closest ID I've found so far, I'm not 100% sure it's pumilio either.