Mapsicon is a free collection of maps for every country in the world, available in 11 different sizes, from 16x16 pixels to 512x512 pixels.
I've tried to sell these icons last year - it was a complete failure. I guess people are not interested in paying for them. This is why I've decided to open source those icons. The only thing I would ask of you, if you happen to use them, is to give me credits on your website. That's it.
If you need to access all those countries programmatically, here is a gist containing all the countries as well as their ISO code: https://gist.github.com/djaiss/2938259