[acheron]

If you ignore Cold War fallout (though the breakup of Yugoslavia continues to this day), and sham countries like South Ossetia, then there's at least Timor-leste and South Sudan. Timor is not in great shape, but appatently getting better, and certainly better off independent. Remains to be seen if South Sudan is better off by itself or not, but I'm not planning a vacation there any time soon.

[rjsw]

There are also the Czech Republic and Slovakia which split up peacefully.

[sheltgor]

As I said, maybe one since the Cold War. I knew South Sudan, but didn't think about Timor-leste. So if you take out the various eastern bloc states breaking up that's only two new countries.