I like to have at least one stamp from every country in the world. Today I received (via ebay) my first stamps from Timor Leste.
This leaves only three countries tofind.
Georgia is easy and cheap to obtain via ebay. Turkmenistan is also easy and cheap but too many issues from there have little to do with the country itself (Lady Diana for example).
War-torn South Sudan only became independent in the past few years. I have seen them on ebay but supplies are irregular and the stamps can be expensive.