[quote=Giant]
See: Sealand, Sahrawi Republic, etc.
[/quote]

Sealand is not legally a country, though. It claims to be, but it is not recognized by any state. You can't say "I'm a country" and automatically become one.

I hadn't heard of the Sahrawi Republic, but quick research revealed that it's only a partially recognized state. By the looks of it, it's in a very complicated situation where many countries have recognized it, but a lot have also either not recognized it, or withdrawn their recognition. It's not really comparable to Sealand though.